When we think of sunscreen, we usually think of sticky days at the beach and white noses, but what is that white stuff and why do we need it anyway?

History

The idea of sun protection arose in the late 1800s alongside the discovery that prolonged sun exposure would allow the ultraviolet (UV) rays from the sun to damage our skin. However, it was the physical effects of sunburn that would motivate Franz Geiter to create one of the first sunscreens in 1946 and to later develop the Sun Protection Factor (SPF) scale in 1962. His goal, to develop a cream that would protect the skin from burning and other UV damage, has been the purpose of sunscreen as long as it has existed. 

UVA vs UVB Rays

Most sunscreens today are listed as “Broad Spectrum,” meaning they protect against both ultraviolet type-A (UVA) and ultraviolet type-B (UVB) rays. UVB rays are probably the ones you’re more familiar with, as they are responsible for giving you a sunburn, but they’re also the main cause of skin cancer, including melanoma. UVA rays also contribute to the formation of skin cancers, but mainly they lead to premature aging (photoaging). Wrinkles, fine lines, and sun spots are the result of exposure to UVA rays. 

An important distinction between UVA and UVB is their prevalence in sunlight, and their penetration ability. UVA is 500 times more prevalent in sunlight than UVB; thus, sun exposure can still damage the DNA in your skin cells, even without a sunburn. Also, UVA has a longer wavelength, allowing it to penetrate deeper into the skin and to penetrate standard glass, like that in your windows, while UVB is blocked.

Sun Protection Factor (SPF)

SPF measures the amount of UVB rays required to burn skin that is protected from the sun, relative to the amount of UVB required to burn bare skin. Simply put, the SPF number of a sunscreen indicates the amount of UVB one can be exposed to before burning; the higher the SPF, the more protection. Keep in mind that the intensity of sun exposure varies throughout the day and depends on your location and skin tone, so the amount of SPF required is very individual. 

To get an idea of what SPF you should use, keep this in mind, SPF 30 allows 3% of UVB rays through to your skin, while SPF 50 allows only 2% of UVB rays through, and SPF 100 allows 1% of UVB rays to penetrate. Beyond the SPF 30 point, the increase in protection is somewhat marginal, which is why the American Academy of Dermatology (AAD) recommends using sunscreens with an SPF of 30 or higher day-to-day use for all individuals. All sunscreen, no matter the SPF, must be reapplied throughout the day to provide maximum protection, as higher SPF sunscreens do not protect you longer than lower SPF sunscreens.

Mineral vs Chemical Formulations

The two main types of sunscreens are mineral (also called physical) and chemical sunscreens, with each blocking the sun differently. Mineral sunscreens use inorganic filters that deflect and scatter the sun’s rays. Behaving like a reflective shield, mineral sunscreens are typically less cosmetically appealing as they can leave a white cast, though they are regarded as safer for more sensitive skin types. Chemical formulas use organic filters that absorb the sun’s rays and convert the energy into heat, but don’t worry, you don’t feel hotter because of it! They are made with cosmetic appearance and feel in mind, usually applying clear and absorbing into the skin easier.

There has been debate over the safety of oxybenzone, avobenzone, octisalate, octocrylene, homosalate, and octinoxate, the main ingredients in most chemical sunscreen formulas. The FDA recently concluded that the body absorbs these ingredients, however it has not been determined whether or not the absorption of these chemicals is harmful to the body, and more research is required to determine the safety of these ingredients. 

This same study classified the main ingredients of mineral sunscreens, titanium dioxide and zinc oxide, as “generally recognized as safe and effective,” meaning the safety and efficacy of these ingredients is confirmed. Even desiring more safety research, the authors of the study supported the continued use of both chemical and mineral sunscreens.

Sunscreen Application

The most crucial part of using sunscreen isn’t the type of sunscreen you use, it’s how you use it. There are three important aspects of sunscreen application:

• How much to apply

• When to apply

• Sunscreen Reapplication

How Much Sunscreen?

The recommended amount of sunscreen is that which makes the SPF label accurate, which is about two milligrams of sunscreen per square centimeter of exposed skin. For the entire body, this is enough to fill a shot glass. Applying to the face only, this is about the size of a nickel. 

When Do I Apply It?

Every day! You probably already wear sunscreen if you are going to be outside in the sun for a good amount of time, but you should also be wearing sunscreen when you’re out running errands, when it’s shady, and even when you’re inside (because of those pesky UVA rays!)

I Have to Reapply?

Yes, and dermatologists recommend you reapply every two hours to maintain your level of SPF protection all day. An important note, if you have been sweating profusely or have gone swimming, you should use sunscreens that specifically state they are water-resistant, and Water-resistance only lasts 40-80 minutes depending on the sunscreen, so read the instructions and be sure to reapply as necessary.

The most important aspect in choosing a sunscreen is choosing one you will use everyday. Frequent use of sunscreen prevents skin cancer, fends off sunburn, and halts premature aging, all to make your time in the sun enjoyable now and in the future!