Sunburn causes one of the most common injuries to the human skin. It results from overexposure to ultraviolet rays, damaging the tissues of the skin. The nerves become inflamed, causing pain; the small blood vessels become injured, causing redness, swelling and leakage of plasma, which results in blister formation.

The amount of ultraviolet light the skin has received is difficult to gauge accurately. Not until after exposure (4-12 hours later) does the redness, tenderness and discomfort of sunburned skin confirm the person's judgment error.Most people with normal skin can be adequately protected against burning by using a commercial sunscreen. However, certain individuals are so sensitive to the sun that they cannot be sufficiently protected by such preparations. The best "sunscreen" for these people is probably four walls and a roof. Opaque clothing provides better protection than the best chemical sunscreens.

To help individuals select an effective sunscreen, the system of rating products by the "skin protection factor" (SPF) has been developed. The higher the SPF number, the greater the protectiveness against sunburn. Individuals who usually burn easily and severely require a sunscreen with an SPF of 15 or higher.

Choosing a sunscreen should be guided by the person's skin type and prior sun exposure. The likelihood for sunburning lessens during the summer, since the normal tanning response of the skin provides subsequent protection. Sunscreen effectiveness also is determined by how much is applied - the more the better.

Suntanning can create a sense of well-being in most people, and the skin produces vitamin D after sun exposure. However, these benefits must be weighted against the negative effects - wrinkling, pigmented spots, atrophy, elastic tissue damage, etc. In short, sunlight is hazardous to the skin, especially in the development of skin cancer.

Simple guidelines for suntanning without burning include:

1. Midday exposure. Avoid exposure at least from 10 a.m. until 2 p.m. when the sun's short ultraviolet rays - the burning rays - are at their peak.

2. Sunscreens. These don't keep you from getting a tan; they only lessen the likelihood of burns.

3. Cloudy-day burns. Some of the worst burns occur on days when the sun is not shining brightly.

4. Temperature tricks. You may feel cool because of the cooling effect of the water and lake breeze and still get a bad burn.

5. Water. Ultraviolet rays penetrate water. A burn can still result even if you spend the day immersed in water.

6. Medications. Some drugs cause an increased sun sensitivity.

7. Vacations. If you have not been exposed to the sun and are going into a sunny climate, try to get two to three weeks of gradual exposure before you leave.

If you have become sunburned:

- Avoid any further exposure to the sun.

- If your eyes are affected, contact your doctor.

- Keep the sunburned area cool. Do not apply ice, since this may result in frostbite.

- Aspirin is extremely effective in relieving the inflammation and pain and should be used unless your doctor instructs you to the contrary.

- If blisters break, thoroughly wash the area twice daily with soap and water and then cover with sterile gauze to prevent infection.

- Application of a cream (e.g., Noxema) will help keep the skin moist.

- Drink lots of water during the acute period of sunburn and eat only light foods.

- If the burn becomes infected, contact your doctor.