02 October 2022
Sunscreen protection, as you might know, is dependent on firstly, the amount that the user applies and secondly, whether the user reapplies it in 3-4 hour intervals. If you’re using less than adequate amounts of sunscreen; the realised protection against UVA and UVB rays would be lesser than expected. So if you’re using, say, half the amount of sunscreen that you need, the expected SPF protection of your sunscreen is also less than the stated value. Sunscreens also lose their effectiveness in 3-4 hours, so reapplication is recommended to provide continued protection against UV rays.
Do you use enough sunscreen; and do you reapply sunscreen after 3-4 hours? As a doctor who is obsessed with her sun protection, I must admit that I fall short on reapplication as it can be challenging when you’re out and your skin isn’t clean. The second problem with sunscreen is that very frequently, people do not use enough sunscreen, rendering their sunscreen protection less than adequate1.
Enter UV detection stickers. These are little purple stickers that can tell a user whether the sunscreen application has been adequate; and reminds the user to reapply sunscreen in a few hours. Interestingly, these UV stickers have also been used beyond their original purpose (of reminding the user to reapply sunscreen) to evaluate the efficacy of sunscreen by TikTokers. My interest in these UV stickers (and anything sunscreen related) was piqued, so I purchased the brand of UV stickers that’s viral on TikTok, SpotMyUV to try. So welcome to yet another review of Things Rach Buys from TikTok!
UV stickers that are trending on TikTok are little circular stickers that are pasted on the skin before sunscreen application. Before sunscreen application, the UV stickers are purple in colour in the presence of UV light. After sunscreen application, these UV detection stickers turn colourless. When the sunscreen’s effectiveness wears off, the UV stickers turn purple again. This colour change serves to remind the user to reapply sunscreen.
There are a couple of different brands of UV stickers that are available. I bought my UV detection stickers from SpotMyUV, as this was the brand that was trending on TikTok and online media. Most of the UV stickers across the different brands are largely similar in their colour change and response to sunscreen.
Each SpotMyUV sticker consists of 3 layers:
• Top: Patented keratinous layer that mimics the skin, called Dermatrue.
• Middle: Photochromic dye that turns purple in UV light. When UV light is blocked out by sunscreen, the dye changes to colourless in the presence of visible light.
• Bottom: Adhesive layer in direct contact with the skin. This adhesive layer is waterproof and hypoallergenic.
To use SpotMyUV stickers, simply stick it on any part of your body. I chose to stick mine on my arm. Before sunscreen application, each SpotMyUV sticker is purple. Apply sunscreen on your body, as well as on your SpotMyUV UV sticker. Wait for the sticker to change colourless and you’re good to go. When the sunscreen’s effectiveness has worn off, the middle layer of the UV detection sticker comes into contact with UV light and turns back to purple. When sunscreen is reapplied again, the UV sticker turns purple.
The good about SpotMyUV UV Stickers
With its highly visible colour change, SpotMyUV stickers definitely served its purpose of reminding me to reapply sunscreen. The UV sticker was easy to use and adhered to my skin for a full day. Despite sweating from an outdoor run and showering, my SpotMyUV sticker clung on. I did not experience any irritation or redness from where the SpotMyUV sticker adhered on my skin.
The UV detection stickers were weightless and I barely noticed it was stuck on my arm. I even turned up for an evening cocktail event with the sticker on because I did not realise it was not removed.
The bad about SpotMyUV stickers
There are a few issues in the product design that limit SpotMyUV’s UV stickers’ ability to truly represent the interaction of sunscreen and UV rays on human skin. These limitations may lure the user into a false sense of security if they delay their sunscreen reapplication if they were to rely solely on the UV stickers as a reminder.
First of all, the uppermost Dermatrue layer mimics the keratinous layer of the top layer of human skin. However, it is not skin. The Dermatrue layer of SpotMyUV UV sticks does not contain the adnexal structures that are naturally present in human skin. Meaning, it lacks structures such as the pilosebaceous unit and sweat glands. The implication of this is that Dermatrue does not mimic physiological processes and dynamics of how skin interacts with sunscreen. Sweat washes off sunscreen and causes sunscreen to redistribute on the skin2; and the Dermatrue model does not account for such interactions. Hence, users may get a false sense of security when using UV stickers as the Dermatrue still retains sunscreen while the surrounding skin does not.
In this respect, my personal experience with SpotMyUV stickers also highlighted this weakness. The colour change for SpotMyUV stickers was very slow for me. It took more than 30 minutes for the UV stickers to change from purple to colourless after sunscreen application. After a run in the afternoon sun and shower (I made sure to thoroughly wash off all sunscreen); my UV sticker remained colourless! I was skeptical of the UV detection sticker’s reading and reapplied sunscreen anyway.
Secondly, SpotMyUV stickers give an indication of UV rays for a specific spot. It is not representative of whether other parts of the skin are equally protected. So if your UV sticker indicates that your skin at that particular spot is protected; you may or may not have the same UV protection on the skin of the rest of your body, depending on the amount of sunscreen applied or reapplied.
Lastly, you might have seen these UV stickers being used to evaluate the effectiveness of sunscreen protection on TikTok. As part of their sunscreen reviews, TikToks use this colour change to assess whether a sunscreen gives broad spectrum UV protection. If the UV sticker turns colourless, the sunscreen gets their approval. But if the UV sticker remains purple despite sunscreen application, the sunscreen in question gets flak for providing less than adequate protection. Consumer trust in the sunscreen brands that don’t turn the UV stickers completely colourless will definitely be eroded, if we were to look at this at face value. Doesn’t this remind you of the Korean sunscreen controversy from 2 years ago?
This intent of using stickers to evaluate a sunscreen’s spectrum of protection is beyond the original intent of the creators of SpotMyUV stickers. While using SpotMyUV stickers to review sunscreen may be TikTok worthy, this rudimentary method is very different from formalised testing for sunscreen in laboratories. SpotMyUV stickers indicate a colour change for a photochromic dye in the presence of UV light. Factors such as the amount of sunscreen used can be arbitrary. Formal assessments of UVB and UVA protection assessment of sunscreen looks at the minimal erythematous dose and minimal pigmentary dose respectively. These assessments require standardisation of variables such as UV dose and amount of sunscreen; and are calculated with equations. Using SpotMyUV stickers is not a precise or accurate way to evaluate a sunscreen’s protection.
As someone who is already cognisant of reapplying enough sunscreen when needed, I did not need these UV stickers. Also, SpotMyUV stickers did not seem to turn back to purple after I washed off my sunscreen! If your SpotMyUV stickers work for you (mine definitely did not), these UV detection stickers are definitely a useful visual reminder for sunscreen reapplication. However, the UV sticker does not function like skin and the inherent limitations of its components, there may be instances where the sticker does not change to purple colour when it should and the reminder is not seen. UV stickers are also not representative of the UV protection on the rest of your skin; so you’ll need to be aware of reapplying enough sunscreen on your skin that is exposed to the sun.
1. Sunbathers’ application of sunscreen is probably inadequate to obtain the sun protection factor assigned to the preparation. Bech-Thomsen and Wulf. Photodermatol Photoimmunol Photomed. 1992;9(6):242-4.
2. In vitro skin model for characterization of sunscreen substantivity upon perspiration. Keshavarzi et al. Int J Cosmet Sci. 2021 Jun;43(3):359-371.