Steve Thompson, Contributing writer

When you're excited to jump in the pool or head to the beach for an afternoon of playing in the sun, you might glance at the bottle of SPF 30 in your bathroom and wonder whether it is really necessary. After all, how much damage can the sun do in just a few hours of exposure?

According to the Palo Alto Medical Foundation, 20 percent of Americans will eventually suffer from some type of skin cancer. Although other lifestyle and environmental factors impact a person's risk of skin cancer, sun exposure hovers at the top of the list of causes. The foundation claims that the best way to protect yourself against skin cancer is through prevention, which includes the use of sunscreen. Whenever you will be out of the house and exposed to the sun, slather on some protection just in case.

How Does It Work?

There are several active organic and inorganic ingredients in sunscreen, according to the Library of Congress, that help to battle damage caused by UV-A and UV-B sun rays. UV-B rays are generally associated with sunburns, while UV-A rays penetrate deeper into the skin, potentially causing lasting damage.

Inorganic ingredients in sunscreen such as zinc oxide are responsible for either reflecting or scattering UV radiation, while the organic ingredients absorb it. It is a good idea to purchase broad-spectrum sunblock because these products are designed to ward off both UV-A and UV-B rays.

What Is SPF?

SPF stands for sun protection factor. It measures the amount of light required to burn skin in the midday sun. A higher SPF product provides more protection than a lower SPF one; experts recommend a minimum of SPF 30 for children. However, these numbers have climbed in recent years, with sunblocks offering SPFs as high as 100 today.

It is important to realize that SPF is not the only indication of a sunscreen's ability to protect the skin. Broad-spectrum products are more effective because they guard against UV-A and UV-B rays, while other products are formulated to be water-resistant for fun in the ocean or pool.

When To Wear?

Most people know to put on sunscreen when they take a trip to the beach or an amusement park where they will endure long exposure to the sun. However, sunscreen might be necessary more often than you think. For example, a cloudy day does not protect your skin against the sun's rays. Cloud cover might reduce heat, but it does not obstruct UV-A and UV-B rays. Any time you are outside, sunscreen is recommended, but especially when long exposure is possible.

Experts recommend applying sunscreen at least 30 minutes before going outside to give the lotion time to sink into the skin. It should then be applied every two to three hours, depending on exposure. Contrary to popular belief, SPF is not related to the amount of time that can safely lapse between applications.