Fun in the Sun!
Are you using the right sunblock? Which types to choose...
Chemical or Physical?The UV radiation in sunlight consists of UV-A, UV-B, and UV-C rays. UV-A and UV-B are both responsible for photoaging, skin cancer, sunburn, tanning, and wrinkling. UV-C is not a factor in skin health, as it is absorbed by the Earth's atmosphere and does not reach us in significant amounts. Broad-spectrum sunscreen protects against both UV-A and UV-B. This protection can work in one of two ways: chemical or physical.
Chemical UV FiltersWork by absorbing UV radiation; Require application 30 minutes before sun exposure; Provide partial protection from UV spectrum; May irritate the skin and eyes; Not regulated for safety by the US Food and Drug Administration (FDA)--some may even be carcinogenic; Not photostable (exposure to sunlight degrades effectiveness); Avobenzone is the most commonly used chemical filter ingredient.
Physical UV FiltersWork by reflecting UV radiation; Start protecting immediately upon use; Provide full broad-spectrum protection; Non-irritating to skin and eyes; Safe, as particles do not penetrate the skin; Highly photostable (exposure to sunlight does not change effectiveness).
Zinc oxide and titanium dioxide are the most commonly used physical filter ingredients. Clothing and shade structures also count as physical filters.
How Stable Is It?One of the most important factors in the effectiveness of a sunscreen formula is also one of the least known to the general public. Photostability is an ingredient's ability to remain effective after exposure to sunlight. Many people are aware that this is an issue for numerous skin care ingredients, but may be surprised to learn that some active ingredients in sunscreen--a product whose sole purpose involves being exposed to sunlight--are not photostable. In addition, the FDA's new rules do not require sunscreen ingredients to be tested for photostability. Yet, many consumers expect that their sunscreen will protect them for longer than one hour. Physical filters such as zinc oxide and titanium dioxide are photostable. Studies have shown that these ingredients suffer no degradation after more than two hours of sun exposure. However, the chemical filter avobenzone is not at all photostable, and degrades almost completely in less than one hour. Even worse, avobenzone also degrades on contact with other UV filters such as zinc oxide or titanium dioxide, and with metal ions such as iron oxide, which is commonly found in makeup. This goes a long way toward explaining why many consumers experience sunburn even after applying sunscreen as directed.