Sun exposure is the No. 1 cause of premature aging; it can also be deadly. Each year, more than one million Americans are diagnosed with skin cancer, the most common of all cancers. About 50,000 of these cases involve melanoma, which is the most serious form of skin cancer. If not treated promptly, melanoma cells can spread to other parts of the body and prove fatal.

Overexposure to sunlight can also exacerbate wrinkles and age spots and dilate blood vessels. It also can alter the skin’s texture to look older as well as damage the eyes. Skin conditions such as lupus can worsen with prolonged sun exposure. People who take certain medications, such as antibiotics, blood pressure medicines or retinoids are more sensitive to the sun's rays.

The sun is harmful to all skin types, but people with lighter skin that freckles easily are at greatest risk. Another risk factor is a family history of skin cancer.

Although skin cancer is less prevalent among people with darker skin, some, especially Latinos, are developing skin cancers at an increased rate. Asians and African Americans are not immune to melanoma, either. When it does appear, it's often found on the palms, on the soles of the feet or under the fingernails.

The three most important reasons to limit exposure to the sun are the risk of developing skin cancer, faster aging and interactions with certain medications.

There are three main types of skin cancer: basal cell carcinoma, squamous cell carcinoma and melanoma. Basal cells are the most common, but melanomas are the most deadly. All can result from too much exposure to ultraviolet rays.

Chronic exposure to the sun’s ultraviolet rays can lead to the development of non-melanoma skin cancers. Sporadic, high-intensity sun exposure can lead to the development of melanomas.

There is some crossover, but this is often the case. Essentially, ultraviolet rays damage the skin and overwhelm the body's natural repair mechanisms.

The sooner you get out of the habit of excess sun exposure, the better. It may sometimes seem as though this does no good because the damage previously incurred is still developing. Eventually you will reap the benefits.

UCI Health dermatologists have many methods to help patients. There are creams, laser treatments and fillers that can go a long way toward returning the skin to peak condition.

The key to sun protection is to use “broad spectrum” products that protect the skin from both ultraviolet A and B rays.

Look for a sunscreen with a minimum sun protection factor (SPF) of 30 to protect against ultraviolet B (UVB) rays. Also look for suncreens containing zinc oxide, titanium dioxide, avobenzone, mexoryl or helioplex to protect against ultraviolet A (UVA) rays, which penetrate the skin more deeply, are responsible for premature aging and contribute to the development of skin cancer.

Baby oil, cocoa butter or similar products should be avoided. They do not protect the skin from ultraviolet rays.

Apply generously. It takes about one ounce (two tablespoons) of sunscreen to cover the entire body. As a rule of thumb, a pea-sized amount should cover an area about the size of your palm. At least 80 percent of skin cancers occur on the head and neck, mostly due to day-to-day exposure to the sun. Get in the habit of putting sunscreen on in the morning after you brush your teeth.

For best results, apply sunscreen at least 30 minutes before significant sun exposure. Reapply sunscreen every 2 hours, and apply more often if you are swimming, exercising or sweating.

Hats and tightly woven clothing also are protective. Some companies make clothing with sun protection factor (SPF) ratings. As a rule, light-colored, lightweight and loosely-woven fabrics offer minimal protection from the sun. For example, white cotton T-shirts provide an average ultraviolet protection factor (UPF) of 7. A green cotton T-shirt offers 10 UPF. On the other hand, thicker fabrics such as velvet may provide 50 UPF.

Specially treated fabrics are now used in some lightweight clothing that offers protection from UVA and UVB. These clothes have been specially treated with UV-absorbing dyes that provide 50 UPF or more. There are also laundry additives containing a sunscreen that can last through numerous washings.

Avoid the sun between 10 a.m. to 4 p.m., use sunscreen and wear sun-protective clothing.

Sometimes it's best to think of your day upside down: If you normally go to the beach in the afternoon and the movies at night, think about making a switch. There is nothing quite as fine as walking along the beach as the sun goes down, and movie theaters are much less crowded in the afternoon.