How Does Sunscreen Work?

By Marisa Ramiccio. May 7th 2016

Before you step outside, do you slather sunscreen on your skin? Many people have made putting on sunscreen a part of their daily regimen, along with brushing their hair or getting dressed in the morning. For years, dermatologists and beauty experts have recommended this practice because sunscreen is one of the best protectors from the sun. But how does sunscreen actually work?

How Sunscreen Works

Sunscreen is used to protect skin from the sun’s harmful rays, which are known as ultraviolet rays. There are two types of UV rays that sunscreen can fight against:

  • UVA – This wavelength is the longest and can penetrate the skin, causing immune system problems and premature aging.
  • UVB – This wavelength is shorter than UVA and is most responsible for causing sunburn.

Both of these rays are damaging to the skin and prolonged exposure to them can cause wrinkles, mottled skin and even skin cancer. To prevent these types of skin damage, many people wear sunscreen, of which there are two types:

  • Physical sunscreen – This type of sunscreen can also be referred to as sunblock. Although many people use the terms “sunscreen” and “sunblock” interchangeably, sunblock is actually a type of sunscreen and it works in a different way. Sunblock reflects UVA and UVB rays and blocks them from penetrating the skin. In the past, sunblock was characterized by its white color, produced from zinc oxide. But nowadays, many types of sunblock aren’t visible on the skin.
  • Chemical sunscreen – This type of sunscreen uses a mixture of organic and inorganic ingredients to absorb and scatter UV rays. Oftentimes, sunscreens only absorb UVB rays but there are some that absorb and dissipate UVA rays as well.

Active Ingredients

Both physical and chemical sunscreens use key ingredients called active ingredients. Active ingredients are the chemicals that reflect, absorb and scatter the sun’s UV rays. The active ingredients in physical sunscreen are:

  • Zinc oxide
  • Titanium dioxide

The active ingredients in chemical sunscreen are:

  • Avobenzone
  • Benzophenone
  • Cinnamates
  • Ecamsule
  • Anthranilates

Sunscreens are comprised of many other ingredients such as dyes and fragrances that can cause an allergic reaction. Other ingredients such as PABAs, parabens, oxybenzone, retinyl palmitate and propylene glycol can cause photosensitivity, dry skin and other harmful effects, so if you are worried about using these chemicals, look for a sunscreen that does not contain them.

How To Choose The Best Sunscreen

Aside from the ingredients, there are a few other things to consider when choosing the best sunscreen. The first thing is SPF, or sun protection factor. The SPF measures how well the active ingredients absorb UVB rays. There is no standard for measuring the absorption of UVA rays. The SPF number is calculated by how long the manufacturer believes it will take sunscreen-slathered skin to burn.

Typically, dermatologists recommend using an SPF of at least 30. Higher SPFs of 45 or 60 are also available, but may not work better than SPF 30 due to variables such as how much sunscreen is used and how much is washed off from water or sweat.

Another important factor to consider is whether or not the sunscreen is broad-spectrum, which means that the sunscreen protects against both UVA and UVB rays. Since you want your skin to be protected from all UV rays, it’s best to choose a broad-spectrum sunscreen.

Types Of Sunscreen

Sunscreen comes in many different forms including:

  • Lotions
  • Creams
  • Sprays
  • Wax sticks
  • Powder

Generally, no type of sunscreen works better than another, so choosing a sunscreen is really a matter of preference. The one type of sunscreen you don’t want to use is the one that’s been sitting in your cabinet for the past decade. Sunscreens do expire and while they can work for up to three years, it’s recommended that you throw away any sunscreen that’s past the expiration date.

Tips For Applying Sunscreen

It doesn’t matter what brand or type of sunscreen you use if you don’t apply it correctly. Here are some tips on how to properly put on sunscreen:

  • Apply a generous amount of sunscreen to your body at least 20-30 minutes before going outdoors.
  • Be sure to cover all areas that will be exposed to the sun including ears, lips, hands, legs and feet.
  • Make sure the skin is well-coated and the sunscreen is rubbed in thoroughly. The recommended amount to use is about one ounce or 30 milliliters.
  • Sunscreen doesn’t last forever, so reapply it every two hours and reapply it after swimming or sweating profusely.
  • Make sure children as young as six months old are wearing sunscreen or, if younger, are kept in the shade.
  • The sun’s rays are always beaming down on Earth, whether it’s the middle of summer or the dead of winter, so always wear sunscreen even if the temperature is a bit cooler.

Even though wearing sunscreen is a great way to protect your skin, it’s not the only way and works best when combined with other measures such as wearing protective clothing and hats, and staying in shaded areas during the sun’s peak hours of 10am to 4pm when possible.


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