1. What patch-sensor adhesion is (the short version)

In this article a patch sensor means a small wearable sensor stuck to the skin to measure things such as glucose in interstitial fluid, sweat, the electrocardiogram or temperature (our own working definition). How the sensing works is covered in other articles in this series. Here we focus on the layer that holds the sensor to the skin.

• Role: 3M's technical paper says that the success of stick-to-skin wearable monitoring devices depends heavily on accuracy and design, and on secure attachment to the body for the whole required wear time Sourced
• Why it is hard: A review by Heikenfeld and colleagues (2018) says that many of the difficulties of wearable sensors become understandable once the skin is seen as "more of an information barrier than an information source" Sourced. For adhesion too, skin moves, sweats, produces oil, carries hair and renews its surface
• The trade-off: The adhesive must hold while the patch is worn and be gentle when it is removed. "Sticks" and "peels cleanly" are two sides of the same material properties (Commentary)

2. The layers of a patch: body, tie layer, backing, adhesive

A skin-worn device is not made with one adhesive. 3M's paper divides the jobs adhesives do into three: covering and protecting, bonding to a device, and bonding two substrates together Sourced. In Avery Dennison Medical's wear study, a plastic disc standing in for the sensor body (a sham device) is fixed with tie-layer tape to a skin-adhesive patch, and the patch surrounds the body in a "skirt" arrangement Sourced. The company says this configuration mirrors the wear characteristics and designs of commercial wearables such as continuous glucose monitors (CGMs).

View the original SVG schematic, source notes and numerical details

The three skin-adhesive tapes Avery Dennison Medical tested use the same pressure-sensitive acrylic skin adhesive and differ only in the backing (carrier). MED 5740 has a white thermoplastic polyurethane nonwoven, MED 5741 a white polyester (PET) nonwoven, and MED 5742 a clear 1 mil (about 25 µm) polyurethane film Sourced. The company notes that the three products differ in breathability (moisture vapor transmission), adhesion level and the elasticity of the carrier Sourced. The adhesive family and the finished tape, backing included, have to be considered separately.

The general character of acrylic, rubber and silicone adhesives is covered in this series' articles on tapes and silicones, and the principle that wetting comes first and strength later in the article on adhesives. This article concentrates on what changes when those ideas meet a very particular adherend: skin.

3. Skin adhesive families: acrylic, silicone, hydrocolloid and others

3M's technical paper names three main families of pressure-sensitive adhesive (PSA) for stick-to-skin wearables: acrylic, silicone and synthetic rubber. It adds specialty formulations such as conductive hydrogels and hydrocolloids, which are designed to wick moisture Sourced. The paper also says synthetic rubber adhesives bond strongly to low-surface-energy materials and, for that reason, are often the first choice for bonding the construction layers inside a device rather than for the layer that touches skin Sourced.

Acrylic versus silicone: how they flow, and how stiff they are

3M explains the difference between the two families in terms of how well they wet the skin and how they deform at removal Sourced.

• Acrylic: A traditional acrylic adhesive is slow to wet out and conform to the contours of the skin, and at first touches only the high points. Over time it flows into skin texture and around hair, so adhesion rises, and so does the chance of pulling hair and stratum corneum off at removal. Acrylics are stiffer and deform less, so the skin is pulled harder at removal, the paper says
• Silicone: Silicones have low surface energy and, more importantly, low modulus, so they wet out quickly and form a maximum bond. They are more elastic than traditional acrylics, especially over long timescales, which avoids cold flow around hair and skin cells. At removal the adhesive deforms, causing less trauma to the stratum corneum, according to the paper

3M's paper also shows confocal microscope images of the adhesive faces of medical tapes after removal from a healthy volunteer, with a qualitative difference in the amount of skin cells transferred between acrylic and silicone (the paper adds that results vary with the application) Sourced. This is the series' idea of the "adhesive as a slowly flowing solid" (tape article) and of the low surface energy and low modulus of silicone (silicone article), applied to skin (Commentary).

The structure of a hydrocolloid

According to the abstract of a patent publication [Reference 17], a hydrocolloid adhesive is a composition with hydrocolloid particles dispersed in a rubbery elastomeric base (US 4,952,618, assigned to 3M; we make no reading of claim scope) Sourced. When the material takes up water, the hydrocolloid swells. A review by Thomas (2008) says the impermeable nature of hydrocolloid wound dressings allows washing or showering while helping to prevent the spread of pathogenic microorganisms Sourced. That one material both takes up water and blocks water vapor becomes important in the chapter on sweat and moisture.

4. A materials engineer's view 1: skin is not a steel plate

All Sourced (Table 1 of the Avery Dennison Medical white paper; typical values, i.e. the manufacturer's stated values). TDS-01 and the rest are the company's own test-method codes; temperature, speed, dwell time and MVTR test conditions are not given in the paper. All three use the same pressure-sensitive acrylic skin adhesive and differ only in backing.

The skin's side of the interface

3M's paper explains that the outer stratum corneum is continually shed and replaced, and that on average the skin renews itself about every 14 days Sourced (the company's statement; the renewal period varies with site and age). Renewal slows with age, moisture falls, and the skin becomes drier, thinner and more fragile. The paper divides "fragile skin" into four groups Sourced.

• Physiological: infant skin, elderly skin, and fragile zones such as the face and eyelids
• Pathological: acne, atopic dermatitis, rosacea and the like
• Circumstantial: environmental (heat, cold, chemicals) and mechanical (rubbing) stress
• Iatrogenic: medicinal treatment and aesthetic procedures

So the surface being bonded to varies widely with age, body site and health, and cannot be controlled like a material. From the designer's side, no single adhesive is optimal for everyone. That is why 3M suggests that a device meant for the whole population might use an adhesive portfolio covering a range of adhesion levels Sourced.

5. Wear time and removal: a 14-day wear study as an example

"How many days will it stay on" is answered not with a steel-plate number but by sticking the product on people and measuring the time until it comes off. Avery Dennison Medical's white paper is one of the few that publishes the design and results of such a test. It is, however, the company's own technical paper (not peer-reviewed), it tested the company's products, and it used sham devices rather than real sensors Sourced.

All Sourced (Avery Dennison Medical white paper [Reference 2]; the manufacturer's own results; products MED 5740, 5741 and 5742).

In the white paper's Fig. 3 (survival curves), all three tapes begin to lose devices after day 10, and the curves fall by day 14. Reading off the figure, the share still attached on day 14 looks like roughly the 60-80% range (our visual reading of the figure; the paper states no numbers). In its discussion the company also says that wear time could extend beyond two weeks depending on conditions, user environment and product design Sourced, but that is the company's view, not a result of this study.

6. What happens at removal: skin injury (MARSI) and the force numbers

Many of the problems after application arise at removal. A consensus statement by McNichol and colleagues (2013) called skin injury from medical adhesives a prevalent but under-recognized complication, and named it medical adhesive-related skin injury (MARSI) (based on a consensus meeting of 23 experts; the meeting was funded by an unrestricted educational grant from 3M) Sourced. A later consensus paper (LeBlanc and colleagues, 2019) describes the definition as erythema or other skin abnormality (vesicle, erosion, tear and so on) that persists 30 minutes or more after removal of a device containing adhesive, and the types as mechanical, dermatitis and other Sourced.

Peel force versus pain and skin burden: two studies

Is it true, then, that the weaker the peel force, the gentler the adhesive on skin? Two studies show that the answer is not simple.

(1) Klode et al. (2011): force and pain did line up

In the study of 56 wound dressings mentioned above, the median energy needed to remove a dressing from skin was hydrocolloid 2.25 N, acrylic 1.14 N, polyurethane 0.9 N and silicone 0.7 N (as written in the abstract, which gives the unit as N). Pain on removal (visual analogue scale, 0-10) was 6.8 for hydrocolloid, 4.9 for acrylic, 3.1 for polyurethane and 2.5 for silicone, with a significant correlation between adhesion and pain (correlation coefficient 0.806, P = 0.01) Sourced. The authors point out that no standardized test procedure exists for investigating the adhesion of wound dressings Sourced.

(2) Turnbull et al. (2024): force and stratum corneum removal did not line up

A study in Cureus by researchers at 3M compared four commercial medical tapes (two with silicone adhesive and two with acrylic; one of them a product of the authors' employer) on 88 healthy volunteers (32 on the back, 56 on the forearm) Sourced.

• Adhesion: 24 hours after application, each tape was pressed with a 4.5 lb roller and removed on a peel tester at 180° and 90 inches/min. One silicone tape adhered most strongly and one acrylic tape least, so there were differences within a family as well
• Stratum corneum removal: adhesion force did not correlate with the total protein or corneocytes removed. Silicone tapes removed less than acrylic tapes (the most strongly adhering silicone tape carried 31% to 74% less total protein than the other three)
• Skin barrier: after ten successive applications and removals on the forearm, transepidermal water loss (TEWL) showed no significant difference from untaped skin for the silicone tapes, while it rose significantly for the acrylic tapes
• Inflammation marker (IL-1α): results were confounded by position on the forearm and no overall conclusion could be drawn

The authors list as limitations the small number of tapes and the fact that the subjects were healthy volunteers rather than fragile skin. They also offer, as a conjecture, that for the acrylic tape with a plastic backing, which adhered least and disrupted the barrier most, a plastic backing may trap moisture and interfere with adhesion.

In a separate study, Waring and colleagues applied six wound dressings to the backs of healthy volunteers over 15 days, with removal and reapplication, and reported that the change in transepidermal water loss (TEWL) ranged from almost none to a rise of about 28 g/m²/h depending on the product (abstract) Sourced. Both point the same way: even under the single name "adhesive", the effect on skin changes greatly with the product's design (the combination of adhesive and backing).

7. Our calculation: unit conversions and the order of magnitude of moisture transmission

8. Sweat and moisture: between breathability and adhesion

Skin continuously gives off water vapor, and exercise and heat add sweat. A patch sits on top of that for days. Moisture acts in two directions.

• It weakens adhesion: Avery Dennison Medical says skin produces sweat, oil and hair, all of which affect adhesion Sourced. 3M likewise says that adhesive selection should consider the user's activity, sweating and climate Sourced
• It can macerate the skin: moisture trapped between skin and tape can lead to a different type of skin injury, maceration (Fig. 4; Commentary)

In patch design the backing's moisture vapor transmission rate (MVTR) is an important variable. Even with the same adhesive, Avery Dennison Medical's three tapes differ by about 3.7 times: 1000 g/m²·24h with the PET nonwoven, 400 with the thermoplastic polyurethane nonwoven and 270 with the polyurethane film Sourced Our calculation (typical values stated by the manufacturer; test conditions not given). Static shear (resistance to slipping), on the other hand, was longest for the film backing with the lowest MVTR, at 1120 minutes, about 4.3 times the 260 minutes of the PET nonwoven Sourced Our calculation. With the same adhesive, the choice of backing moved breathability and resistance to slipping in opposite directions (Commentary).

Yet in the 14-day wear study the three came out without significant difference, as described above. That is, differences in MVTR and shear measured in the laboratory do not necessarily appear in whether a device stays on. The white paper's data do not tell us which property decides the wear result (Commentary).

A hydrocolloid is a rubbery base with water-absorbing particles dispersed in it, and it takes up water and swells (chapter 3). 3M describes hydrocolloids as gentle, cushioning and absorbent, and lists water resistance among the features of silicone Sourced. Even under the one phrase "good with water" there are families that soak it up and families that repel or pass it, and the design thinking differs (Commentary).

9. A materials engineer's view 2: four demands that work against each other

10. Evaluating irritation and sensitization: ISO 10993 and FDA guidance

An adhesive that touches skin for a long time is evaluated for three biological effects: cytotoxicity, sensitization and irritation. The framework is the ISO 10993 series (biological evaluation of medical devices). The series is not a list of tests to pass. It is a framework in which the kind and duration of contact determine which effects to evaluate, and the result is judged as risk.

All Sourced (the official pages of the standards body EVS [References 10-14]. The ISO site itself could not be fetched automatically, so numbers, titles and scope were confirmed on the page of an ISO member body. The full text of the standards is paid and was not checked).

Kinds and durations of contact: FDA guidance

The FDA guidance "Use of International Standard ISO 10993-1" (issued 8 September 2023; nonbinding recommendations) categorizes devices by kind of contact (surface device on intact skin, mucosal membrane and so on) and by contact duration. The durations are limited (24 hours or less), prolonged (more than 24 hours to 30 days) and long-term (more than 30 days) Sourced. Its Attachment A (Table A.1) lists, for a surface device on intact skin, cytotoxicity, sensitization, and irritation or intracutaneous reactivity as endpoints to consider in all three duration categories Sourced. The guidance says the table is a framework and not a checklist for testing, and that different endpoints may warrant evaluation for particular devices.

Sensitization tests: mostly animal methods

The guidance says the sensitization tests most often submitted are the guinea pig maximization test (GPMT) and the local lymph node assay (LLNA). For devices that only touch the skin (topical devices) the Buehler method may also be used, per ISO 10993-10. For novel materials it is not known whether chemicals will penetrate the skin in an LLNA, so the LLNA is not recommended and the GPMT is Sourced. These are animal tests; they do not directly examine whether a given person will react (Commentary).

The revision to ISO 10993-1:2025: FDA's explanation as of 2026

ISO 10993-1 was revised in 2025 (the sixth edition). According to the record of a town hall held by FDA's CDRH on 9 September 2026 Sourced:

• Devices are now categorized by tissue type (intact skin, intact mucosal membrane and so on), and the "externally communicating device" category was removed. For FDA submissions, however, that term may still be used
• FDA partially recognized the new edition in May 2026. Declarations of conformity to the 2018 edition will be accepted until 1 July 2029. FDA does not plan to update its guidance now and says that its expectations for biocompatibility testing are not raised by the 2025 edition

This article did not check how the revision changes the evaluation of skin-contact adhesives in detail, because the text of the standard is paid.

Standard testing does not rule out individual reactions: case reports

Biocompatibility testing assesses hazard for a population. It does not guarantee that no individual will react. In fact, there are case reports of allergic contact dermatitis caused by isobornyl acrylate (IBOA, an acrylate) at the application site of a continuous glucose monitor. Mine and colleagues (2019) report an 8-year-old girl with type 1 diabetes who had a positive patch test to the adhesive part of the sensor and to IBOA at 0.1%, 0.05% and 0.01% Sourced. Similar case reports exist (Corazza et al. 2018; Kamann and Oppel 2019), and a report (Oppel et al. 2020; by its title) describes a successor model as an IBOA-free generation Sourced.

11. A materials engineer's view 3: FDA treats adhesives as a separate case

12. Adhesion test methods: steel, skin and wear studies

The test methods that have appeared so far, arranged by what they look at.

"90 inches/min = about 38 mm/s" is our conversion Our calculation (90 × 25.4 ÷ 60 = 38.1). Everything else is Sourced (see each reference).

A steel test has a uniform adherend and high reproducibility. A skin test differs between people, between body sites and between days. Avery Dennison Medical's white paper takes the position that both kinds of test are needed and neither replaces the other. For a materials engineer, that means designing and reporting tests that control the material's quality (steel) separately from tests that reproduce how the product is used (skin, wear), and always attaching the adherend, site, preparation, time and speed to the result (Commentary).

13. Open issues and what could not be confirmed

(1) No independent source comparing the families under the same conditions

Among the sources this article consulted, we could not confirm any study that compares acrylic, silicone, hydrocolloid and other families under the same conditions and is independent of adhesive suppliers. 3M and Avery Dennison Medical supply adhesive materials, and the authors of the Turnbull study work at 3M. The Klode and Waring studies concern wound dressings. This article introduces the character of each family but does not declare one better than another.

(2) Avery Dennison Medical's white paper is not peer-reviewed

The 14-day wear study is the company's technical paper: 20 healthy adults, sham devices, one center, and no justification of statistical power is given. Apart from being pressure-sensitive acrylic with different backings, the composition of MED 5740 to 5742 could not be confirmed.

(3) The text of the standards was not checked

The text of the ISO 10993 series and of ISO 29862 and others is paid. Because the ISO site refused automated access, titles and scope were confirmed on the standards body's (EVS) official pages and in the FDA guidance. We did not check how ISO 10993-1:2025 changes the evaluation of devices that touch skin in concrete terms. We also did not check the related Japanese standards (the JIS T 0993 series) or the treatment under Japan's Pharmaceuticals and Medical Devices Act.

(4) The adhesives of actual wearable-sensor products are out of reach

The adhesive composition, layer structure and wear-test data of commercial continuous glucose monitors and similar products could not be confirmed in the public official material this article consulted. The numbers here come from studies of sham devices, commercial medical tapes and wound dressings. For a product's wear time and the frequency of skin reactions, one must consult each product's instructions for use and the regulator's documents.

(5) The skin renewal period is the manufacturer's statement

"Renews every 14 days on average" is 3M's statement, with no source given. The period varies with age, body site and health.

(6) No source quantified the effect of sweat volume or exercise

The studies consulted did not restrict showering or exercise, but we could not confirm any result that quantified the relationship between sweat volume and detachment.

14. Glossary

15. References

1. 3M "Designing Wearable Devices for Fragile Skin" (Medical Materials & Technologies technical paper, © 2021) — multimedia.3m.com
2. Avery Dennison Medical "Adhesives Enabling Reliable, Multi-Week Wearable Device Attachment" (white paper, © 2020) — medical.averydennison.com
3. Turnbull MJ et al. (3M) Comparison of Medical Tape Performance Using Skin Response Quantitative Measurements on Healthy Volunteers. Cureus 16(3): e56548 (2024). DOI 10.7759/cureus.56548 (CC BY 4.0, PMC11027027) — doi.org
4. Klode J et al. Investigation of adhesion of modern wound dressings: a comparative analysis of 56 different wound dressings. J Eur Acad Dermatol Venereol 25(8): 933-939 (2011). DOI 10.1111/j.1468-3083.2010.03886.x (abstract checked on PubMed, PMID 21062365) — doi.org
5. McNichol L et al. Medical adhesives and patient safety: state of the science: consensus statements for the assessment, prevention, and treatment of adhesive-related skin injuries. J Wound Ostomy Continence Nurs 40(4): 365-380 (2013). DOI 10.1097/WON.0b013e3182995516 (abstract checked on PubMed, PMID 23759927) — doi.org
6. LeBlanc K et al. Peristomal Medical Adhesive-Related Skin Injury: Results of an International Consensus Meeting. J Wound Ostomy Continence Nurs 46(2): 125-136 (2019). DOI 10.1097/WON.0000000000000513 (PMC6519893) — doi.org
7. Waring M et al. An evaluation of the skin stripping of wound dressing adhesives. J Wound Care 20(9): 412-422 (2011). DOI 10.12968/jowc.2011.20.9.412 (abstract checked on PubMed, PMID 22068140) — doi.org
8. U.S. Food and Drug Administration (FDA) Guidance "Use of International Standard ISO 10993-1, 'Biological evaluation of medical devices - Part 1: Evaluation and testing within a risk management process'", 8 September 2023 (nonbinding recommendations; Attachments A and G) — fda.gov
9. FDA (CDRH) "Biocompatibility Town Hall #1: Risk Assessment Approaches for Addressing Biocompatibility Endpoints", transcript, 9 September 2026 — fda.gov
10. EVS (Estonian Centre for Standardisation and Accreditation) ISO 10993-1:2025: title, scope and edition history — evs.ee
11. EVS ISO 10993-5:2009 Tests for in vitro cytotoxicity — evs.ee
12. EVS ISO 10993-10:2021 Tests for skin sensitization — evs.ee
13. EVS ISO 10993-23:2021 Tests for irritation — evs.ee
14. EVS ISO 10993-12:2021 Sample preparation and reference materials — evs.ee
15. Heikenfeld J et al. Wearable sensors: modalities, challenges, and prospects. Lab Chip 18(2): 217-248 (2018). DOI 10.1039/C7LC00914C (abstract checked on PubMed, PMID 29182185) — doi.org
16. Thomas S Hydrocolloid dressings in the management of acute wounds: a review of the literature. Int Wound J 5(5): 602-613 (2008). DOI 10.1111/j.1742-481X.2008.00541.x (abstract checked on PubMed, PMID 19134061) — doi.org
17. U.S. patent US 4,952,618 "Hydrocolloid/adhesive composition" (Minnesota Mining and Manufacturing Co; inventor Roger A. Olsen; granted 28 August 1990; abstract only) — patents.google.com
18. Mine A et al. Allergic contact dermatitis caused by isobornyl acrylate when using the FreeStyle Libre. J Diabetes Investig 10(5): 1382-1384 (2019). DOI 10.1111/jdi.13023 (abstract checked on PubMed, PMID 30758915) — doi.org
19. Corazza M et al. Allergic contact dermatitis caused by isobornyl acrylate in a young diabetic patient using a continuous glucose monitoring system (Freestyle Libre). Contact Dermatitis 79(5): 320-321 (2018). DOI 10.1111/cod.13075 (title only checked, PMID 30039529) — doi.org
20. Kamann S, Oppel E Hydrocolloid blister plaster decreases allergic contact dermatitis caused by Freestyle Libre and isobornyl acrylate. Contact Dermatitis 81(5): 380-381 (2019). DOI 10.1111/cod.13329 (title only checked, PMID 31148185) — doi.org
21. Oppel E et al. Freestyle libre 2: The new isobornyl acrylate free generation. Contact Dermatitis 83(5): 429-431 (2020). DOI 10.1111/cod.13638 (title only checked, PMID 32542740) — doi.org
22. ISO ISO 29862:2024 Self adhesive tapes — Determination of peel adhesion properties (checked for this series' tape article) — iso.org
23. ASTM International ASTM D3330/D3330M-04(2025) Standard Test Method for Peel Adhesion of Pressure-Sensitive Tape — store.astm.org
24. Japanese Standards Association (JSA) JIS Z 0237:2022 Testing methods of pressure-sensitive adhesive tapes and sheets (title translated from Japanese) — webdesk.jsa.or.jp
25. ISO ISO 29863:2018 Self adhesive tapes — Measurement of static shear adhesion (checked for this series' tape article) — iso.org

16. Claim-to-source audit

Last updated 3 October 2026. Sources are limited to primary material (technical papers from adhesive-materials manufacturers, peer-reviewed studies, FDA guidance and records, and official pages of standards bodies). Values from manufacturers' documents are treated as the manufacturer's stated values or the company's own test results, and no family or product is declared better than another. Because the article includes structural readings and materials-design interpretations, those are marked as Commentary and kept separate from sourced fact. The adhesive composition and wear-test data of actual wearable-sensor products, independent same-condition comparisons of families, the relationship between sweat volume and detachment, the concrete changes in ISO 10993-1:2025, and the related Japanese standards and legal treatment are not stated, because no published primary source could be confirmed. All figures are explanatory concept graphics. Figs. 1 to 7 are vector drawings; the hero image and Fig. 8 are AI-generated images, and none of them shows a real product, testing machine or cross-section. This article explains materials, evaluation and regulation and is not medical advice.