Sunscreens help to prevent sunburns and skin cancers because they actually block the ultraviolet rays of the sun that damage the skin. However, some sunscreens are safe, while others may not be safe. Sunscreens are classified as those that contain:
• Absorbers: chemicals that absorb the sun’s rays, so that less pass through to the skin
• Blockers: minerals, primarily zinc oxide and titanium, that block some of the sun’s rays.

The chemical sun ray absorbers are more effective than the mineral blockers, and therefore they comprise most of the sunscreen market today. However, several of the chemical sun ray absorbers have “endocrine disrupters” that may increase cancer risk (Int J Androl, Jun 2012;35(3):424-36) and are absorbed rapidly into the bloodstream (JAMA, May 6, 2019). We have known this for more than 23 years (Lancet, 1997;350(9081):863-864). Dermatologists who have been among the strongest supporters for the regular use of sunscreens to help prevent skin cancer are now very concerned about the harm that some of the ingredients may cause (J Am Acad Dermatol, 2019;80(1):266-271; Dermatol Clin, 2019;37(2):149-157). The FDA has already concluded that the risks for chemical absorbers such as para-aminobenzoic acid (PABA) and trolamine salicylate outweigh their benefits and has proposed classifying them as unsafe.

The mineral blocker sunscreens, such as zinc oxide and titanium, appear to be very safe. They are potentially dangerous only if small particles are inhaled, and that is unlikely to happen with sunscreen lotions or creams.

Protecting Yourself from Sunlight
The most effective protection from UV light is a roof, and then clothes. Sunscreens are the least protective, but they are better than nothing.
Clothes are far more protective than sun screens. Wear a hat that covers your ears and shades your face. Shirts made from lightweight moisture-wicking materials can be used in hot weather to keep you covered and cool. With short-sleeve shirts, you can use “arm coolers” that block the sun’s rays and evaporate sweat rapidly. Pouring water on the arm coolers will make you feel even better. You can buy arm coolers in sports stores or online. Dark colored fabrics block UV rays better than light colors; the colors that block the most UV include black, deep blue, orange and red. Tightly woven fabrics block more UV than looser weaves. Hold the material up to a light source; the more light that passes through a fabric, the more UV will also pass.
Sunglasses: Skin cancers around the eyes, mouth, ears and nose are among the most difficult to treat and cure and are also the ones most likely to recur after treatment. Cancers in these areas can tunnel underneath the skin and not be obvious to the naked eye. Sunglasses block UV light and therefore help to prevent cancer in skin around your eyes.
Sunscreen Application: Sweating, swimming, or a single brush of your hand can remove the sunscreen. Apply a sunscreen so you can see it on your skin and then reapply that sunscreen at least every hour or two. Make sure that you apply sunscreen to the areas with the most exposure to sunlight over your lifetime: the top of your ears, nose, your face, the back of your neck, and your arms and hands. To meet your daily vitamin D requirements from sunlight, you can expose your legs or other areas of your body that have received little cumulative sun exposure over your lifetime.

Sun Protection Factor (SPF)
The SPF on sunscreen labels tells you how long it takes to burn your skin underneath that sunscreen. It does not tell you how much protection you are getting. The sun’s skin-damaging rays are classified into UVA, UVB, and others, of which UVB is the most potent to cause sunburn and skin cancer. A SPF 30 sunscreen blocks 97 percent of UVB rays, compared to an SPF 15 sunscreen that blocks 93 percent. No sunscreen blocks all UV rays.

Broad-spectrum sunscreens provide some protection against UVA and UVB rays, but the SPF rating refers only to the level of protection from UVB rays. The U.S. Food and Drug Administration (FDA) ruled that sunscreen labels that claim to be “broad spectrum” must protect against UVA as well as UVB. These rules also prohibit any sunscreen from claiming that it prevents skin cancer or aging because no sunscreen blocks all UV rays. Sunscreens cannot claim that they last for more than two hours, unless proof of longer protection is submitted to the FDA. There is no advantage to choosing sunscreens just because they have an SPF greater than 60. The FDA has shown that you do not need a sunscreen with an SPF greater than 30.

Sun Protection Myths
• Clouds do not protect you. Up to 80 percent of the sun’s UV rays can pass through clouds.
• Glass does not protect you completely. Glass blocks UVB rays that are the primary causes of skin cancer and sunburns, but it does not block UVA that can also cause skin cancer and aging.
• Beach umbrellas do not protect you as much as you might think. UV rays are reflected toward you from sand and water. Studies show that you get up to 84 percent of the exposure to UV radiation under an umbrella that you receive in the open sun.
• Dark skin does not protect you completely. People with darker skin still need to follow sun protection precautions. Skin pigment reduces the amount of UV rays that pass into skin, but it does not prevent sunburns or skin cancer.

Don’t Waste your Money on Sunscreen Pills
The FDA warns that no pills on the market today prevent sunburns and skin cancers from excessive sun exposure because they do nothing to block harmful ultraviolet rays. They are only antioxidant pills called polypodium leucotomos that may increase the time it takes for people to burn their skin when exposed to ultraviolet rays. Excessive exposure to the sun damages the skin and the dying skin cells release oxidants that cause redness, swelling and pain called inflammation. These pills contain antioxidants that can delay some of the redness, itching and pain, but they do not prevent sunburns or skin cancers. The FDA writes that companies claiming that their pills prevent skin damage from excess sunlight are “putting people’s health at risk by giving consumers a false sense of security that a dietary supplement could prevent sunburn, reduce early skin aging caused by the sun, or protect from the risks of skin cancer.”

Also see: EWG’s annual guide to sunscreens
My summary on skin cancer and its prevention