How to Buy Sunscreen

UVA, UVB and sunblock

Sunscreens are available in a variety of preparations (sprays, lotions, creams) and potencies (SPFs typically range from 15 to 100). Some things to know before you buy: Ingredients are directly connected to protection. There are two types of ultraviolet (UV) rays that can harm skin: UVB light causes common surface sunburns, while UVA light triggers deeper connective-tissue damage (like premature aging and skin cancer). In addition, there are two kinds of skin-damaging UVA rays -- short waves and long waves. Experts say a good sunscreen should protect users from both UVA and UVB rays, each of which is responsible for different levels of skin damage.

Long-wave UVA rays penetrate the skin to deeper levels causing unseen damage that can eventually result in premature aging and skin cancer. These UV rays are always present in sunlight, in equal degrees, regardless of the time of day or year. Short-wave UVB rays are responsible for reddening of the skin and sunburns. They vary in intensity with the time of day, season and location.

Additionally, the SPF rating listed on sunscreens applies only to UVB rays -- currently, there is no rating system in the United States for UVA rays though one should be in place by 2012.  Experts say that, for the most part, SPF 15 is suitable for everyday use, and SPF 30 is recommended for extended periods of sun exposure. Higher SPF ratings are also suitable, but overall, experts say they don't offer any extra protection.

Instead, to best protect yourself, experts suggest looking at a product's ingredients. They say titanium dioxide, zinc oxide, avobenzone (Parsol 1789), Mexoryl SX and Tinosorb (outside of the U.S.) are the only ingredients that can effectively block long-wave UVA rays. Titanium dioxide and zinc oxide are mineral sunscreens that sit on top of the skin and effectively block both UVA and UVB rays. Avobenzone, Mexoryl SX and Tinosorb are chemical sunscreens that absorb UVA rays before they can cause damage to the skin. Other active sunscreen ingredients, including homosalate, octisalate, octinoxate, octocrylene and oxybenzone, block UVB rays and short-wave UVA rays.

Here are some other things experts say about sunscreen:

• The No. 1 cause of skin damage is sun exposure. Therefore, reviewers recommend your sunscreen contain no less than an SPF 15 for daily use and no less than an SPF 30 for extended periods of sun exposure. Sunscreen should include UVA protection with titanium dioxide, zinc oxide, avobenzone or Mexoryl SX (or Tinosorb outside the U.S.). The SPF factor only indicates UVB (or surface sunburn) protection, and an SPF greater than 30 doesn't offer any better protection from UV rays. Sunscreen should be worn any time you are outside, regardless of how long you will be out, and it should be reapplied frequently (every two hours or every 40 to 80 minutes if swimming or perspiring, even with water-resistant sunscreen).

• No sunscreen is truly waterproof. In 2002, the Food and Drug Administration (FDA) mandated that manufacturers change their labels from waterproof to "water resistant" or "very water resistant," because no product can be completely waterproof. Not all manufacturers have made this change. Water-resistant formulas protect against sun damage for 40 minutes while in the water, and very water-resistant formulas protect for 80 minutes.

• For the best protection, apply sunscreen 30 minutes prior to exposure. Sunscreen can take up to 30 minutes to dry and become effective enough to reduce the effects of sun exposure. It's also important to follow the directions about the amount required to fully protect the skin.

• Sunscreen SPF ratings on the bottle are only realized when you apply enough product. Experts say that adults should be using 1 ounce of sunscreen for full-body coverage. This is the equivalent of approximately 2 tablespoons or a palm-full. Experts say that most people do not apply enough sunscreen and that this is the most common mistake that people make.

• Some medications (such as skin creams or lotions containing alpha hydroxy acids or topical retinoids) can significantly increase an individual's sun sensitivity. To head off potential problems, check with your pharmacist about medications before heading outside, and carefully read cosmetic labels.

• Children should wear UVA/UVB sunscreen because their skin is more sensitive than adults'. The American Academy of Pediatrics advises avoiding sun exposure and dressing infants or children in lightweight pants and long-sleeved shirts as a first defense, but it says sunscreen can be used on infants less than 6 months old, if adequate shade and clothing aren't available. Titanium dioxide and zinc oxide are the gentlest UVA-protective ingredients for children's more sensitive skin.

• Antioxidants can increase the efficiency of sunscreen. They do not protect against sunburn, but studies show that antioxidants in combination with broad-spectrum sunscreen protect against cell damage better than antioxidants or sunscreen alone.

• Sunscreen on top of sunscreen doesn't equal more SPF. If you wear makeup with SPF in addition to sunscreen, the result is an SPF that equals the highest contained in the two products. Because sunscreens can clog pores and cause breakouts, experts say that women with oily skin may prefer to use a foundation with a good SPF on their faces and a good sunscreen from the neck down.

• Unless otherwise noted on the bottle, sunscreen is good for about three years from the date of purchase.

• Ideally, sunscreen should be applied daily to the face, neck and hands, whether or not you will be outdoors. UVA rays can penetrate through windows (ever gotten sunburned while driving?). In fact, experts say that not wearing sunscreen daily for a year is equivalent to an entire week at the beach without sunscreen.

• Consider taking a vitamin D supplement; direct sunlight is the best source of vitamin D. Although experts don't agree about whether sunscreen prevents vitamin D absorption, many say direct sunlight creates too much of a risk of skin cancer. If you're concerned, talk to your doctor about taking a supplement instead.