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Sunscreen vs Sunblock: What are they and how do they work?


It feels great to be outside on nice days. But your skin might not be enjoying it as much as you are! The sun can do lots of damage to your skin if you aren't careful, but it can be hard to know how to protect yourself. In this post, we'll look at sunscreen and sunblock — what are they, how do they work, and which should you use? Learn how to protect yourself and your family from sunburn and UV light damage all year round.

Are sunscreen and sunblock the same thing?

man with sunscreen on his back

You've probably heard "sunscreen" and "sunblock" used interchangeably. But they are actually two different products! Sunscreen is a chemical that absorbs into your skin, where it attracts harmful UV rays before they can damage your cells. Sunblock is a protective barrier that sits on top of your skin. It blocks UV rays from reaching you at all.

Which are you using? Check the ingredients label on your products! Examples of sunscreen ingredients include:

  • Avobenzone
  • Oxybenzone
  • Para-aminobenzoic acid (PABA)

For sunblock, look for zinc oxide or titanium oxide on the label.

Should I use sunscreen or sunblock?

woman sunbathing on a beach

Both sunscreen and sunblock are effective at protecting your skin from harmful UV rays found in sunlight. However neither product can stop 100% of rays from reaching you and damaging your skin. Unless you never go outside (or too near a window) it's impossible to avoid UV light completely.

Many products now use both sunscreen and sunblock ingredients in their formulations. This gives you the best chance of avoiding the most UV damage possible. But not everybody can tolerate every ingredient in sunscreen. If you have:

  • sensitive skin
  • rosacea
  • allergies

you might find sunscreen irritates your skin. Sunblock will deliver better results, without causing any side effects. This is also why sunblock is used more frequently in products aimed at children.

The main downside to sunblock is the white, chalky residue it leaves behind. Because it's a protective layer that sits on your skin, it will be a little noticeable. You'll need to use sunscreen if you want invisible UV protection.

The other consideration is Sun Protection Factor (SPF). Only sunscreen has an SPF rating. Learn all about it now!

What is SPF?

a woman faces into bright sunlight

SPF is a number from 1 to 100 that tells you how well a product protects against UVB rays. There are three types of UV rays, A,B, and C.

UVC rays are the most harmful, but they get absorbed by the ozone layer and don't reach us. UVB rays are the next most harmful. These rays are the ones most associated with causing skin cancer. UVA rays are less harmful, although they cause surface damage to our skin. UVA rays are likely responsible for many signs of premature aging, such as wrinkles and liver spots.

SPF only measures UVB protection. It tells you how much more UVB exposure you can have before burning when you use the product, compared with using no sun protection at all. So if you burn to a crisp in 10 minutes outside without sunscreen, with SPF 15 you can have 15 times more exposure before burning.

Is SPF a measure of time?

the bright sun sets in an orange sky

SPF is not a measure of time, but of UV exposure. That's an important distinction. You might think if you can be out for 10 minutes before burning without sunscreen, then SPF 15 will let you stay outside for 150 minutes (15 x 10). But it isn't that simple.

The amount of UV light that the sun releases changes all the time. UV light is strongest during peak sunlight hours, and during the spring and summer months. The worst time to be outdoors is between 10am and 4pm in the summer. That's when UV light is strongest.

UV rays fluctuate in strength. That means you might be able to stay outdoors in the morning for several hours using SPF 15. But by midday you might only be able to stay outdoors for 20 minutes before you start to burn.

It's a good idea to check the UV Index before going outdoors. UV light is measured by the National Weather Service and graded 0-11+ according to a scale used by the World Health Organization.

  • 0-2 Low risk
  • 3-5 Moderate risk
  • 6-7 High risk
  • 8-10 Very high risk
  • 11+ Extreme risk

Even at the lowest levels, the EPA and WHO recommend wearing sunscreen of SPF 30 or higher before going outdoors. On moderate risk days, you should stay out of the sun during the peak hours of late morning through early afternoon. When the UV risk is high, you should stay indoors as much as possible. And on extreme risk days, unprotected skin and eyes will burn in minutes.

Some environmental factors also increase UV risk. White surfaces such as snow, sand, or even buildings, reflect and intensify UV light. People on skiing vacations can get extreme sunburn even on very low risk days because they forget the damage done by reflected light.

How does the FDA regulate SPF?

 young boy applies sunscreen to face beside a swimming pool

All products with SPF ratings have been tested by the FDA to make sure they really do protect skin from UVB light. Remember, SPF doesn't measure UVA light protection! However if you want extra protection, look for "Broad spectrum" on your sunscreen bottle. This means that the product has been tested and shown to offer some protection against UVA rays.

There is no such thing as a "waterproof" sunscreen, and the FDA does not use that term. Instead, the FDA tests for "water resistance" for specific amounts of time. Look for 40 or 80 minute water resistance labels on your sunscreen if you intend to spend the day at the pool or beach or working up a sweat.

No matter what the weather, or what SPF, reapply water resistant sunscreen every 40-80 minutes to stay protected. If your sunscreen has SPF but not a water resistance rating, it isn't suitable for use if you intend to be swimming or sweating.

Why do we need to wear sunscreen all the time?

Do you associate sunscreen with hot, summer days at the beach, sports season, or vacations? It should be part of your everyday routine, all year round. UV light is stronger in the summer, but it doesn't go away in the winter. EPA average monthly UV Indexes show that there is always a risk of UV light exposure. The only exception is Alaska in the winter, when the sun doesn't rise!

What are the signs of sun damage?

older woman with wrinkles smiles in a garden

The first signs of sun damage are pink-red, hot, tender skin. That doesn't mean deeper damage isn't happening before you start showing signs of sunburn. UV light can disrupt our cells and even damage DNA. Our bodies repair a lot of the damage, but not all of it. Over time, it accumulates and results in signs of sun damage and premature aging such as:

  • sun spots, or brown pigmentation on your skin  
  • fine lines around your eyes and mouth
  • deep wrinkles elsewhere on your face
  • rough and blotchy skin 
  • more freckles or moles (especially in children)
  • liver spots and discoloration
  • inflamed or burned corneas
  • cataracts
  • skin cancer

As you can see, protecting your skin from sun damage is about so much more than avoiding unsightly burns. UV light exposure can have serious long term consequences for your skin's health, as well as its appearance.

Can sun damage be reversed?

The damage done by UV light can be healed in some cases, but not reversed. Burned cells slough off and are replaced by healthy new cells. Some skincare products can help hydrate skin, replenish nutrients, and boost collagen and elastin. This can reduce the appearance of wrinkles and discoloration caused by UV exposure. However they cannot completely undo the underlying damage.

No product can totally reverse UV damage. It's too deep, and too widespread. UV light disrupts connections in our cells' DNA and not all that damage can be healed. Over time, that damage accumulates, and will inevitably cause signs of premature aging. That's why sunscreen is so important, because prevention is much more effective than hoping for a cure.

How can I protect my skin from sun damage?

woman applies sunscreen to face

Wear sunscreen! Check the products you use for UV-blocking ingredients, and make sure to use it daily. Remember the FDA regulates SPF, which only measures UVB protection. Look for "broad spectrum" on the label to get UVA protection as well. 

And consider that not all products with UV-blocking ingredients have an SPF rating. Getting that rating requires FDA testing, and some products choose not to go through that process. Especially if they aren't marketed specifically as a sunscreen. Many cosmetic products include UV-blocking ingredients, even if they don't have an SPF rating.

Sunscreen and sunblock are equally effective, so choose the product that's right for your lifestyle, not the one you think you should be using. If your UV protection doesn't fit conveniently into your routine, you're less likely to stick with it. That sunblock isn't the best option if you hate the residue it leaves behind. And it's no good using a sunscreen that interacts with your makeup. Find a product that's easy for you to use, and use it every day. It's the only way to really protect your skin from UV damage when you go outside.

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