In choosing a sunscreen, look at the ingredients. Preparations that help block UV radiation are sometimes classified as sunscreens or sunblocks according to the substances they contain. In general, sunscreens have contained or organic formulas and sunblocks inorganic ingredients.
However, the term sunblock is used less and less as sunscreens increasingly contain both kinds of ingredients:
Organic formulas:
Organic formulas contain UV-filtering chemicals such as butyl methoxydibenzoyl-methane (also called avobenzone or Parsol 1789), benzophenones (dioxybenzone, oxybenzone), sulisobenzone, methyl anthranilate, octocrylene, cinnamates (octyl methoxycinnamate, ethylhexyl p-methoxycinnamate), and terephthalylidene dicamphor sulfonic acid, a UVA blocker. Para-amino benzoic acid (PABA), once a popular ingredient, is now used infrequently. PABA may actually break down in the presence of UV exposure and release harmful oxidants. (And many people have an allergic reaction to it.) Not all these chemicals block UVA, and in choosing an organic sunscreen, people should look for a wide spectrum of chemicals.
Inorganic formulas:
Inorganic formulas contain the UV-blocking pigments zinc oxide or titanium dioxide. Zinc and titanium oxides lie on top of the skin and are not absorbed. They prevent nearly all UVA and UVB rays from reaching the skin. Older sunblocks are white, pasty, and unattractive, but current products use so-called microfine oxides, either zinc (Z-Cote) or titanium. They are transparent and nearly as protective as the older types. Microfine zinc oxide may be more protective and less pasty-colored than microfine titanium oxide.
Inexpensive products work as well as expensive ones with the same ingredients. Unfortunately, there are still not standards for sunscreens, and even those claiming UVA protection may offer very little. In one study, the average UVA protection from a wide range of brands was only 23%. In fact, the average protection on brands not making the claim was 37%.
Organic formulas and inorganic microfine oxides do not protect against visible light, which is a problem for people who have light-sensitive skin conditions, including actinic prurigo, porphyria, and chronic actinic dermatitis. Inorganic sunscreens that protect against visible light and are still cosmetically acceptable are now available in Europe, but not yet in the US.