Adhesive Chemistry and Dermatological Issues in CGMs

Most skin trouble under a CGM falls into one of two kinds. Irritant contact dermatitis is damage from skin kept sealed and damp for days, while allergic contact dermatitis is an immune reaction to one specific chemical [1]. Since 2017, dermatology labs tracing the allergic cases have kept finding the same short list: isobornyl acrylate (IBOA), N,N-dimethylacrylamide (DMAA), a stabilizer called MBPA, and colophonium, a pine rosin [2]. Most of that work tested sensors that have since been replaced, which matters if you're choosing one in October 2026.

Irritant or allergic: why the difference matters

When skin reactions to the first FreeStyle Libre sensor appeared, doctors first blamed irritation from skin temperature, occlusion (the skin being sealed off from air), humidity and long wear [1]. A 2025 review calls irritant reactions probably the more common kind: less severe than allergic ones, and less likely to come back when a sensor goes on a new spot [1].

Allergy works differently. Once the immune system is sensitized to a chemical, the allergy can become lifelong [3]. Dermatologists confirm it with patch testing, which places suspected chemicals on the skin under small patches and reads the result days later [2]. Testing doesn't always settle it. In a Brussels study of 52 people with device reactions, 17 reacted neither to IBOA nor to a piece of their device's adhesive; the authors pointed to an undiscovered allergen or plain irritation [4].

Contact time matters too: the review counts how long and how often a device touches skin among the factors shaping an allergic reaction [1]. As of October 2026, the Dexcom G7 15 Day sensor is worn for 15 days [5], FDA's 510(k) summary says the FreeStyle Libre 3 Plus and 2 Plus sensors stay on with a medical grade adhesive for up to 15 days [6], and MiniMed's Instinct sensor, made by Abbott, lasts up to 15 days [7].

The chemicals behind allergic reactions

Isobornyl acrylate (IBOA)

The story starts with a 2017 paper on the original FreeStyle Libre. All 15 patients with allergic contact dermatitis reacted to the sensor's adhesive part, 12 were sensitized to IBOA, and lab analysis found IBOA in the sensors [8]. Here's what surprised us: the IBOA likely didn't start in the sticky layer. Investigators traced it to the glue joining the two halves of the plastic housing, and the patch maker confirmed that no IBOA was used in the adhesive touching the skin [2].

The American Contact Dermatitis Society named IBOA its Allergen of the Year for 2020 [9]. At Antwerp University Hospital in Belgium, 57 of 1,036 FreeStyle Libre users (5.5%) were referred to dermatology for skin reactions, and 39 (3.8%) had an IBOA allergy [10].

N,N-dimethylacrylamide (DMAA)

DMAA turned up in the same sensor two years later. In a 2019 report on seven patients, six reacted to both IBOA and DMAA and one reacted only to DMAA; lab analysis found DMAA in an extract of the sensor [11]. The two chemicals are often used together, which helps explain why so many patients react to both [2].

MBPA

MBPA, short for 2,2'-methylenebis(6-tert-butyl-4-methylphenol) monoacrylate, is a stabilizer and antioxidant used in adhesives and plastics [2]. It became a problem after Dexcom changed the G6 adhesive in 2019 for better skin fixation. A 2022 German study of five patients with new allergic reactions to the G6 found all five sensitized to MBPA, and none reacted to IBOA [12].

The G6 is a legacy device now. Dexcom says it will no longer manufacture the G6 after July 1, 2026, and it is moving G6 users to its G7 sensors [13].

Colophonium

Colophonium, also called rosin, is a mixture of more than 100 compounds from pine trees, used as a fast-acting adhesive [14]. Among 18 children patch tested at an Italian diabetes center in 2018, it was the most common allergen, found in 41.1% of cases [14]. It also tops a 2025 Antwerp study of 27 patients with reactions to the Guardian Sensor 3 and Guardian 4, now sold by MiniMed. There, 44% reacted to colophonium or its derivatives, 31% to IBOA and 29% to isocyanates [15].

Why switching sensors doesn't always help

For a while, switching looked like a clean fix. A 2019 analysis found IBOA in the housings of the FreeStyle Libre and Medtronic's Enlite sensor but not in the Dexcom G6 [3], and five IBOA-allergic patients wore a Dexcom sensor for at least two days with no reaction [16]. Then a Swedish group found IBOA in the G6 itself. They warned that people sensitized by one device and moved to another are not necessarily free of future reactions [17]. The first two reported cases of allergy to the Dexcom G7, both in children, involved IBOA and colophonium-related substances found in the sensor [18].

In the 2025 Guardian study, every patient allergic to IBOA or DMAA had already been sensitized by the first FreeStyle Libre; patients whose first device was a Guardian sensor weren't sensitized to either chemical [15]. An allergy picked up from one sensor can follow a person to the next. A 2024 systematic review named the core obstacle: device ingredients aren't declared and can change without notice, and commercial patch-test materials haven't kept up [19].

What we know about current sensors

Abbott's FreeStyle Libre 2 and Libre 3 sensors were available only through September 30, 2025, and the Libre 2 Plus and Libre 3 Plus sensors replaced them [20]. As of October 2026, MiniMed's sensor comparison lists the Instinct, Simplera Sync, Guardian 4 and Simplera; Enlite and Guardian Sensor 3 aren't on it [21].

A 2020 analysis of an earlier implanted Eversense system found no IBOA in the sensor, the transmitter or either of its two adhesives [22]. Its successor, Eversense 365, sits under the skin for up to 1 year with an externally worn transmitter [23]; see our article on implantable fluorescence sensors. The Dexcom G7 may have changed as well. A letter published online in Dermatitis in September 2026 refers in its title to a "Dexcom G7 Reformulation" and argues for device ingredient disclosure [24]. In our October 2026 PubMed search, we didn't find a published allergen analysis of the Libre 2 Plus, Libre 3 Plus, Instinct, Simplera, G7 15 Day or Eversense 365.

What's still unknown

The biggest gap is ingredient information. Review authors describe a serious lack of cooperation from manufacturers on sharing ingredients or supplying samples for patch testing [2]. In 2021, 14 contact allergy experts called for EU rules requiring medical devices to disclose and label their composition [1].

Evidence on workarounds is thin. Barrier films helped only two patients at the Antwerp hospital [10], while hydrocolloid or silicone plates under the sensor helped a subgroup of allergic patients in other reports [1]. Whether to patch test, try a barrier or change sensors is a decision to make with your care team. For broader safety reporting on these devices, see our article on adverse events and skin reactions. Until manufacturers publish what their adhesives and housings contain, each new sensor arrives with its allergens unknown.