By using sunscreen, you may be doing your skin a favour, but not marine wildlife.

Four ingredients that routinely appear in chemical sunscreens activate a virus harmful to sea algae, according to a January 2008 study in Environmental Health Perspectives. The chemicals are paraben, benzophenone, cinnamate and 4-methylbenzylidene camphor.

An estimated 4,000 to 6,000 metric tons of sunscreens wash off swimmers annually worldwide, putting 10 percent of coral reefs at risk of dying because they rely on sea algae to stay alive. Researchers encourage sea swimmers to use sunscreens with physical filters that reflect rather than absorb ultraviolet radiation, and to choose eco-friendly sunscreens.

The US-based Environmental Working Group echoes this recommendation. After comparing upwards of 1,100 commercial sunscreens, they suggest choosing mineral-based sunscreens over those that are chemical based. The latter, besides the toxicity concerns of individual ingredients, can generate free radicals that lead to increased risk of skin cancer.

Zinc oxide and titanium dioxide are mineral-based physical filters that offer full spectrum (both UVA and UVB) coverage. These ingredients are frequently the base of non-toxic sunscreens. A rule of thumb when purchasing sun care and other skin care products: The more ingredients you can actually pronounce, the better.

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