Depending on the type of skin pigment a person has and the amount of sun exposure, the skin becomes red, swollen, and painful one hour to one day after exposure. Later, blisters may form, and the skin may peel. Clothing and ordinary window glass filter out virtually all damaging rays. Snow, water, and sand reflect sunlight, magnifying the amount of UV light that reaches the skin. Before exposure to strong, direct sunlight, a person should apply a sunscreen, an ointment or cream containing chemicals that protect the skin by filtering out UVA and UVB rays.
Many sunscreens are either waterproof or water resistant.
Because it takes 30 to 45 minutes to bind strongly to the skin, swimming or sweating soon after applying PABA will wash it off. Occasionally, sunscreens containing PABA irritate the skin, and they can cause allergic reactions in some people. Another type of sunscreen contains a chemical called benzophenone. People who are concerned with appearance can tint these ointments with cosmetics to match their skin color. Sunscreens with an SPF of 15 or more block most UV rays, but no see-through sunscreen blocks all UV rays.