Sunscreen protects skin from harmful ultraviolet (UV) radiation. Many wonder how some sunscreens remain effective when exposed to water. Understanding water-resistant formulations clarifies how they maintain protection during swimming or sweating.
How Sunscreen Stays On In Water
Water-resistant sunscreens are formulated to create a durable layer that resists washing away when wet. This is achieved through hydrophobic (water-repelling) ingredients. These ingredients form a stable film that adheres to the skin.
Film-forming polymers are a key component in these formulations. These include synthetic polymers like acrylates copolymer or silicones, which dry to create a flexible, water-insoluble layer on the skin’s surface. Natural waxes, such as beeswax, also contribute to water resistance by repelling water and forming a protective barrier. These agents ensure the sunscreen’s active ingredients remain distributed on the skin rather than dissolving or washing off.
The formulation process also focuses on effectively dispersing active sunscreen filters within this water-resistant base. Whether mineral filters like zinc oxide and titanium dioxide or chemical filters, they need to be uniformly held within the film. This careful dispersion, combined with the film-forming properties, allows the sunscreen to maintain its integrity and sun protection factor (SPF) even when exposed to water or sweat.
Decoding Water Resistance Labels
Sunscreen labels use terms like “water resistant” or “very water resistant.” These are regulated claims indicating SPF retention after water exposure. These claims are based on specific testing standards established by regulatory bodies like the U.S. Food and Drug Administration (FDA) and international organizations such as ISO.
A “water resistant” label means it retains its SPF for up to 40 minutes of water immersion. A “very water resistant” designation means it maintains SPF for up to 80 minutes of water immersion. This testing involves controlled conditions, where effectiveness is measured after periods of water immersion and drying.
The term “waterproof” is no longer permitted on sunscreen packaging. No sunscreen is truly impervious to water or sweat, and such claims could mislead consumers. The current labeling aims to provide clear expectations about water resistance duration, emphasizing that reapplication is always necessary.
Maximizing Your Water-Resistant Sunscreen Protection
To ensure continuous sun protection, proper application and reapplication of water-resistant sunscreen are essential. Regardless of the water resistance claim, sunscreen should be reapplied regularly, especially after activities involving water or heavy sweating. For “water resistant” sunscreens, reapplication is recommended after 40 minutes of swimming or sweating, while “very water resistant” formulas should be reapplied after 80 minutes. Reapply immediately after towel drying, as this action can remove a significant amount of the product.
Applying a sufficient amount of sunscreen is also important for effectiveness. Most adults need about one ounce, roughly a shot glass full, to cover all exposed skin. Sunscreen should be applied at least 15 to 20 minutes before sun exposure, allowing it to form its protective film before entering the water. Applying it generously and rubbing it in thoroughly helps ensure even coverage.
Water-resistant sunscreen is one part of a broader sun protection strategy. Seeking shade, particularly during peak sun hours, and wearing protective clothing like long-sleeved shirts, wide-brimmed hats, and sunglasses, provide additional layers of defense against UV radiation. These combined measures offer more comprehensive protection for extended periods outdoors.