Three Key Waterproofing Workhorses
1) Film-Forming Polymers
One of the most important ingredients for making sunscreens water resistant is a group of substances called film-forming polymers. These materials create a thin, invisible layer on your skin that helps hold the sunscreen in place, even when exposed to water. This protective barrier prevents the sunscreen from washing away easily, ensuring longer-lasting protection.
2) Acrylic-Based Polymers
Acrylic-based polymers are especially known for their effectiveness in this role. Scientific studies have shown that changing the type of film-forming polymer in a sunscreen can dramatically improve how well it stays on the skin after getting wet. For example, using certain types of acrylic copolymers can boost the water-resistant sun protection factor (SPF) by several times compared to formulas without them.
Other types of film-forming agents, such as modified natural gums and certain synthetic polymers, also help by forming water-repellent layers. Some of these are designed to be especially good at sticking to the skin or creating a barrier that water has trouble penetrating.
3) Emollient Systems That Repel Water
The oil phase (the oily part) of a sunscreen formula is also crucial for water resistance. Different oily ingredients, known as emollients, help the sunscreen stick to the skin and resist being washed off. These systems are similar in function to the oils that coat a duck’s feathers and repel water. Examples include:
Natural waxes like beeswax are classic choices, creating a physical barrier that helps sunscreen adhere better.
Synthetic waxes and oils can often outperform natural options, offering improved water resistance and a more pleasant, less sticky feel on the skin.
Silicone-based ingredients are widely used because they form a flexible, water-repellent film that feels smooth and silky, making the sunscreen more comfortable for daily use.
Certain esters (special types of oils) are also effective. They can form lightweight, non-greasy films that help keep the sunscreen in place, which is especially useful in spray formulas.