Sunscreens are products applied to the skin to protect against the harmful effects of the sun’s ultraviolet (UV) rays.

Many brands of sunscreens are available, containing a variety of ingredients. The active ingredients work by absorbing, reflecting, or scattering some or all of the sun’s rays. Most sunscreen products contain combinations of ingredients. Sunscreen products are sold as lotions, creams, gels, oils, sprays, sticks, and lip balms, and can be bought without a physician’s prescription.

The U.S. Food and Drug Administration requires sunscreen products to carry a sun protection factor (SPF) rating on their labels. This number tells how well the sunscreen protects against burning. The higher the number, the longer a person can stay in the sun without burning. The SPF displayed on the sunscreen label ranges from 2 to as high as 70 and refers to the product’s ability to screen or block out the sun’s harmful rays. Consumers need to be aware that SPF protection does not increase proportionally with an increased SPF number. While an SPF of 2 will absorb 50% of ultraviolet radiation, an SPF of 15 absorbs 93% and an SPF of 34 absorbs 97%.

There are three types of ultraviolet light, based on their wavelength: UVA, UVB, and UVC. UVC has the shortest wavelength and is blocked by the earth’s ozone layer. Concerns about the depletion of the ozone layer focus on the serious health effects that increased exposure to UVC light would have.

UVB light is the next shortest wavelength and is called the tanning light since it is light in this range that promotes creation of the skin pigment melanin that creates a tan. UVB light only penetrates the outermost layer of the skin, but it promotes basal and squamous cell carcinoma and may worsen the effects of UVA.

UVA is long-wave radiation generated by the sun that penetrates more deeply than UVB, causes wrinkling and leathering of the skin and damages connective tissue. UVA is the light that causes melanoma, the most serious skin cancer.

Several types of chemicals are used as sunscreens. They vary by the degree of protection they can provide and the types of ultraviolet light they can block:

• Cinnamates, such as octyl methoxcinnamate, give low levels of protection, and are only effective against UVB light.
• Para-amino benzoic acid (PABA) compounds, including PABA, padimate O  (octyl dimethyl PABA), and glyceryl PABA, are effective only against UVB  light.
• Salicylates, octylsalicylate, and homosalate offer moderate levels of protection against both UVA and UVB light, but the range of light waves against which they protect is relatively narrow.
• Benzophenones, including oxybenzone and dioxybenzone, protect against a broader range of ultraviolet light than the salicylates and are more useful for broad-spectrum protection.
• Physical sunscreens are really sun blockers and include titanium dioxide, red petrolatum, and zinc oxide. Preparations containing these blockers are thick ointments and are usually reserved for skin areas at high risk of burn, such as the  nose.

Other compounds, such as Parsol 1789 (avobenzone), Eusolex 8020, and menthyl anthranilate appear to be valuable broad-spectrum agents. In one study, the combination of 3 percent butyl methoxydibenzoyl-methane and 7 percent padimate O was the most effective of all sunscreens tested.

In addition to the chemical used as a sunscreen, the vehicle can be important in determining how well a product works. Unfortunately, thick, greasy ointments seem to work better than vanishing creams, lotions, or liquids.

Users should carefully read the instructions that come with the sunscreen. Some of these products need to be applied as long as one or two hours before sun exposure. Others should be applied 30 minutes before exposure and frequently during exposure.

Users should apply sunscreen liberally to all exposed parts of the skin, including the hands, feet, nose, ears, neck, scalp (if the hair is thin or very short), and eyelids. However, you should avoid getting sunscreen in the eyes, as it can cause irritation. Use a lip balm containing sunscreen to protect the lips. Reapply sunscreen liberally every one or two hours—more frequently when perspiring heavily. People should reapply sunscreen after they go in the water.

PRECAUTIONS

Sunscreen alone will not provide full protection from the sun. When possible, people should wear a hat, long pants, a long-sleeved shirt, and sunglasses. They should try to stay out of the sun between 10 AM and 4 PM, when the sun’s rays are strongest. The sun can damage the skin even on cloudy days, so people should get in the habit of using a sunscreen every day. They need to be especially careful at high elevations and in areas with surfaces that reflect the sun’s rays, such as off sand, water, concrete, and snow.

Sunlamps, tanning beds, and tanning booths were once thought to be safer than the sun, because they give off mainly UVA rays. However, UVA rays are now known to cause serious skin damage and may increase the risk of melanoma. Health experts advise people not to use these tanning devices.

People with fair skin, blond, red, or light brown hair, and blue eyes are at greatest risk for developing skin cancer. So are people with many large skin moles. These people should avoid exposure to the sun as much as possible. However, even dark skinned people, including African Americans and Hispanic Americans, may suffer skin damage from the sun and should be careful about exposure.

SIDE EFFECTS

The most common side effects are drying or tightening of the skin. This problem does not need medical attention unless it does not improve. Other side effects are rare, but possible. If any of the following symptoms occur, people should check with a physician as soon as possible:

• acne
• burning, itching, or stinging of the skin
• redness or swelling of the skin
• rash, with or without blisters that ooze and become crusted
• pain in hairy parts of body
• pus in hair follicles

The side effects of sunscreens cannot be prevented but can be minimised by testing a sunscreen on a small area of the body before all-over applications.

Anyone who is using a prescription or non-prescription (over-the-counter) drug that is applied to the skin should check with a physician before using a sunscreen.

Sunscreens should not be used on children under six months of age because of the risk of side effects. Instead, children this young should be kept out of the sun. Children over six months of age should be protected with clothing and sunscreens of at least SPF 50, preferably lotions. Sunscreens containing alcohol should not be used on children because they may irritate the skin.

Before using a new sunscreen, particularly a newer formulation, it should be tested on a small area of skin. These products have some risk of causing rashes and other side effects.

Sunscreens should always be applied before a trip to the beach or into some other setting with intense sun exposure. Parents who start to apply sunscreen to their children upon arrival at these settings will exceed their own sun exposure limits before they begin to apply sunscreen to themselves.

Parents should consider using two to three different sunscreens at one time, to get the best results with the fewest problems. Liquids may be best for the scalp, since they can penetrate the hair. Lotions may be most appropriate for most of the body. Ointments may be the best choice for the nose and other parts of the face.

Users should always check expiry dates and not use a sunscreen past its expiry. Reapply sunscreens as directed.