Heat Transfer of Sunscreens: Investigation into the Conductive Properties of Sunscreen

Abstract

Sunscreen is a major preventative product very commonly used for protection against ultraviolet (UV) radiation and the skin cancers associated with extended exposure. There is minimal research into the conductive properties of sunscreen as the major research focus is on radiation effects, but it is still important to understand the impact of sunscreen on the body’s natural heat transfer to the external environment through the skin and extremities, a necessary process to ensure homeostasis. Our research group investigated the conductive properties of sunscreens over two experiments. The first analysed the effect of increasing the thickness of sunscreen on its conductive heat transfer. The results showed that as thickness increased, heat transfer decreased and allowed us to calculate the conduction coefficient (k) for this specific sunscreen sample to be 0.43 W/mK. The second experiment analysed what the impact of combining multiple sunscreens which varied in ingredients, sun protection factor (SPF) and being water or oil based was on their heat transfer. The results allowed us to calculate the thermal conductivity constant (k) for each sunscreen and their mixtures, with Sunscreen B (Brand name Bondi Sands©) having the highest at k=1.34 W/mK, and Sunscreen A (Brand name LeTan©) the least at k=0.27 W/mK. Further, it was found that combining different sunscreens in a 1:1 ratio roughly portrayed that the conductive properties of the mixture was the average of the sunscreen’s properties on their own (For example mixture AB had a conduction coefficient of k=0.70 W/mK). With an understanding of the conductive properties of sunscreen, we can see how exactly its application impacts heat transfer and evaluate if its effects in general are significant, or whether some sunscreens are better for different applications (i.e. ensuring insulative or conductive properties of different sunscreens are used for correct applications).