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Sunscreen 101: How Much Sunscreen To Use and How Long Does It Last

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Everyone is already using their sunscreen daily - right? Great.

But are you sure that you really know how much to use, when to use it, how it works and how long it lasts?

Probably not.

We will guide you through the basics of sunscreen and throw in a few fun sunscreen facts to wow your friends at your next beach outing.

Sunscreen and sun protection basics

Apply sunscreen every day.

Even on the days that you are planning on being mostly inside - over time those little bits of exposure walking to the car or getting the mail add up.

15-minute rule.

The chemicals in sunscreen only work when they are absorbed into the skin, and this can take 15 minutes. So, apply and wait a little before heading out.

Don’t forget to cover all your exposed skin!

We are talking about the easily missed ears, neck, and hands.

And let’s not forget an SPF lip balm!

Throw some shade - in a good way.

The shade is your friend and can significantly reduce the amount of UV rays that reach you.

Embrace the beach cover-up.

Throw on a loose long-sleeved cover-up once you know you have had enough sun. Your skin will thank you later.

Sunglasses are your friend.

The delicate skin around your eyes can be easily damaged by UV rays. And attempting to apply sunscreen closely around your eyes can be a stinging mess.

Wear a large pair of sunglasses when in a sunny situation and your eye skin will be mostly taken care of.


Let’s be honest here - tanning is really just lightly burning and does cause some skin damage that will far outlast that tan.

Avoid intense tanning and burns at all costs for healthier skin in the long run.

When was sunscreen invented?

In 1938 German inventor Franz Greiter got a sunburn at Piz Buin.

This prompted the innovator to develop his Gletscher Crème, or “Glacier Creme”, and sunscreen was invented.

Fun Facts:

This concoction only delivered 2 SPF of protection.

The company made to sell the stuff was named Piz Buin - after the place that Franz got his eureka moment sunburn.

How does sunscreen work?

Sunscreen works by covering your skin in organic and inorganic particles that essentially play goalie with those UV-A and UV-B rays.

Inorganic particles, like zinc oxide, give sunscreen its white color and they reflect or scatter the rays.

Organic particles, like the synthetic carbon-based components, absorb the UV rays and generally convert the energy into heat.

How much sunscreen should you use?

Most people only apply about 25-50% of the recommended amount of sunscreen.

For your face - Aim for a blob of sunscreen about the size of a nickel.

For your body - You need WAY more than you think. Aim for a shot glass-sized amount of the stuff.

What does SPF stand for?

SPF stands for Sun Protection Factor.

And, while you think you know what that means, you may be surprised!

SPF does not mean the amount of TIME that you can be in the sun longer than without sunscreen.

SPF is a measure of how much solar energy is needed to burn you with sun protection applied relative to the amount of solar energy needed to burn you without sun protection applied.

This would be calculated based on many factors including: time of day, location, cloudiness, how much sunscreen you applied, if you went swimming, and your current complexion.

Bottom line:

Please don’t try to calculate this out with a sandy calculator at the beach…

Just aim for at least SPF 30 (Much higher if you are paler - personally, I am no stranger to a 100 SPF) and you should be good.

How long does sunscreen last?

How long sunscreen will last on your skin depends on if you are sweating, if there is something rubbing against your skin (like a pool float), or if you are swimming.

As a general rule of thumb:

Re-apply every 2 hours.


Re-apply immediately after sweating or swimming.

Does sunscreen expire?

Some sunscreen will come with an expiration date printed on the bottle, this may mean that past that point the chemicals have degraded and are not providing you with the same protection as a new bottle.

In this situation, Mayo Clinic advises that you skip the risk and toss the bottle.

If you have a bottle that does not have a date, you can still confidently use it for up to 3 years - as the FDA requires manufacturers to make sure sunscreens remain at full potency for at least 3 years.

Let’s not forget: Medications.

Some medications can increase your sensitivity to the sun and its effects.

Sunscreen is key if you are on one of these medications!

The most common ones are certain antibiotics, blood pressure drugs, cholesterol drugs, and NSAIDs.

Go here for the full list of sun sensitizing medications.

Also included are certain skin and beauty products that contain retinoids.

Our Tretinoin products fall into this retinoid category, so be sure to have your sunscreen handy if you are using the following:

Strut Anti Aging

Strut Acne

Strut Acne Scar

Strut Melasma


Apply sunscreen every day and everywhere!

Give sunscreen 15 minutes to “soak in.”

Cover up with clothing, sunglasses, and get in the shade if possible.

Don’t burn!

German inventor Franz Greiter invented a 2 SPF sunscreen in 1938.

Sunscreen works by reflecting those UV rays or converting their energy to heat.

Use a nickel-sized amount for your face, and a shot glass-sized amount for your body.

SPF stands for Sun Protection Factor, and is calculated based on time of day, location, weather, and your skin tone, among others.

Apply sunscreen every 2 hours, or directly after sweating or swimming.

Toss your old sunscreen after the printed expiration date, or after 3 years.

Apply sunscreen if you are on medications that make you more sensitive to the sun.

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