We do not know how safe sunscreens are because they have never been tested systematically. Oxybenzone in sunscreens has been shown to be absorbed into the bloodstream in humans, and to disrupt hormones in animals. Zinc oxide and titanium dioxide appear to be safe, except that manufacturers often convert them to nanoparticles that can be inhaled. Zinc oxide and titanium dioxide-based sunscreens that do not contain nanoparticles are generally thicker and whiter.
A comprehensive review and critique of more than 1700 sunscreens is conducted each year by the Environmental Working Group. Their findings, with brand name listings and recommendations, are available at Guide to Sunscreens
Since cumulative exposure to sunlight over a lifetime is what causes skin cancers, always cover the areas that have had the most sun exposure: face, tops of the ears, hands and arms. To avoid getting sunscreens in your eyes
• always wash your hands after each application
• do not apply sunscreen above your cheeks,
• use clothes in place of sunscreens whenever you can. Wear a hat that shields your forehead and the top of your ears.
We use “arm coolers” that block the sun’s rays and evaporate sweat rapidly to cool your arms at the same time. They are available at Amazon or on eBay.
If you use sunscreens, be sure to reapply them frequently. Many sunscreens contain the filters octylmethoxycinnamate, benzophenone-3 or octocrylene, which reflect ultra violet rays away from your skin to protect it only when they are on the surface of the skin. However, when these sunscreens are absorbed and the skin is not re-coated, they increase skin production of harmful oxidants that can cause skin aging and cancer (Free Radical Biology & Medicine, September 2009). Reapplying the sun screen so some remains on the skin’s surface can prevent this damage.
• Before you go out in the sun, apply sunscreens to the areas with the most exposure to sunlight over your lifetime: the top of your ears, your face, the back of your neck, and your arms and hands. It is the cumulative exposure to UV light that increases skin cancer and aging.
• To meet your daily vitamin D requirements from sunlight, expose your legs or other areas of your body that have received little cumulative sun exposure over your lifetime. Take care to avoid sunburn.
• Reapply sunscreens every hour or two, particularly when you are swimming or sweating.
• Some sunscreens contain stronger UVA filters (avobenzone, mexoryl, titanium dioxide or zinc) that are less likely to be absorbed into the skin. You do not need to reapply these if they leave a visible white paste on your skin. Check the list of ingredients.