Most of us enjoy a sunny day, and as we grab our sunglasses and dust off our sandals, many of us rely on two common products—sunscreen and insect repellent—to protect our skin from harmful UV rays and the bite of pesky, and potentially dangerous, insects. The latter is particularly relevant in light of the expanding distribution of day-biting insects, such as Aedes aegypti, known to transmit several arboviruses, and sandflies that can transmit leishmaniasis, to name but a few. But a new study has revealed an unexpected consequence when these two products are used together: reduced UV protection.

In a recent research study published in Parasites & Vectors, scientists used an advanced AI-powered deep-learning method called NoxiScore to analyze skin biopsies after applying sunscreen, insect repellent, and a combination of both. The results? When sunscreen and insect repellent were applied together, the UV-blocking power of the sunscreen was significantly impaired.

A deep-learning based pipeline to assess the concomitant use of sunscreen and insect repellents.

The authors describe using ex vivo human skin biopsies in their study, arguing that this simulates real-world conditions in a controlled environment, allowing them to study the direct effects of multiple products, including sun screen and insect repellent combinations, on human skin cells. This potentially provides more accurate and relevant results than the use of artificial or animal models, making this a more reliable and ethical way of studying the toxicity and effectiveness of these products on skin.

The authors applied different combinations of sunscreen and insect repellent on the skin biopsies before exposing them to UVB irradiation in the lab, or to sunlight in real-life settings. The following were tested:

1. sunscreen containing UV filters alone.
2. sunscreen containing UV filters and a mosquito repellent with synthetic active ingredient IR3535 (sunscreen first, followed by a mosquito repellent as often recommended).
3. A commercial preparation of a natural insect repellent plus sunscreen (‘combo’).

The researchers developed and used an image analysis pipeline, starting with the application of the “treatment” to the ex vivo skin biopsies, then the preparation and digitalization of histological samples for the production of high-resolution images and finally the AI-assisted image processing and computational analysis of the data.

The results showed that while sunscreen alone effectively protected against UV exposure, the insect repellent, especially when mixed with the sunscreen, reduced the sunscreen's ability to protect the skin from UVB rays. This could lead to greater susceptibility to skin damage and even increase the risk of skin cancer in the long term.

Food for thought:

This study highlights the importance of considering how multiple products interact and underscores the need for better safety testing of combined products. While insect repellents help prevent insect-borne diseases, and sunscreens protect us from UV-induced skin damage, this research shows that combining the two may compromise both forms of protection. 

The researchers argue that using deep-learning AI delivers precise, consistent and objective cell analysis, rapidly processing large amounts of data and identifying patterns and abnormalities in the skin samples. Because it is an efficient and rapid process it is a scalable analysis method and can provide predictive modelling of how the combination of insect repellent and sunscreen might impact UV protection and overall skin health.  The integration of ex vivo human skin biopsies and deep learning software into a high throughput pipeline is a very innovative approach that could have applications from skin product toxicity to diagnostic and evaluation of numerous skin issues due to exposures and irritants.   

AI statement - I used ChatGPT to help develop an outline for the blog, which I expanded and edited.