When updating a sunscreen formulation to meet today’s requirements, formulators must consider improved water-resistance as a key parameter, since sunscreens are often used outdoors near bodies of water. Reapplication of the product after each water exposure is undesirable for modern consumers who seek both comfort and ease of use from their sun care products. Moreover, the protection provided by a sunscreen can be compromised with sweating; in fact, the reduced efficacy of sun care products due to perspiration has been shown in athletes, where rates of skin cancer have grown.
The term waterproof can no longer accompany sun care products, as it provided an excessive sense of safety to consumers and increased their risk of being burned. Waterproof has been substituted by the claims water-resistant or very water-resistant, when the sun protection provided by a product is reduced by less than 50% after a lukewarm bath lasting 40 min or 80 min, respectively. Many have tried to update this evaluation procedure, including an attempt to develop an in vitro non-human test; however, the traditional in vivo method remains the most adopted.
Water-resistant products are more likely to achieve lower transdermal delivery since their components are contained inside the applied film. This factor allows water-resistant sunscreens to provide longer-lasting protection than standard sunscreen products. In addition, the filters entrapped in the film will have low transdermal delivery to the body, reducing the risk of chemicals penetrating the skin and lowering the accumulation of said substances. Beyond maintaining the efficacy of sunscreens when they come in contact with water, there is also increasing concern related to the accumulation of trace sunscreen ingredients that could harm the resident flora and fauna in lakes, rivers and oceans.