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The SkinSort Blog

Everything Sunscreen pt 2: SPF, PA, Labels

Updated: November 10, 2023

We cannot say this enough: please protect your skin from the sun! Not only does sun damage lead to skin cancer, it also accounts for up to 90% of the signs of aging. According to SkinCancer.org, 1 in 5 Americans will develop skin cancer before they turn 70.

Finding your perfect sunscreen isn’t easy. There are so many things to consider: SPF factor, ingredients, your skin type, and more. The entire process can take some time and research.

We created this guide to help you narrow down sunscreen based on your preferences and values! We’ll explain SPF, UV rays, and what sunscreen labels really mean.

First of all, what are UV rays?

UV rays are a form of electromagnetic radiation from the sun. Other sources of UV rays include tanning beds and welding torches. Radiation is the emission of energy.

The 3 types of UV rays:

  1. UV-A (320-400 nm) contains the least amount of energy.
  • They are linked to the majority of tanning, long term skin damage such as wrinkles and hyperpigmentation, and Melanoma.
  1. UV-B (290-320 nm) rays emit more energy than UV-A rays.
  • They are capable of damaging DNA in skin cells. UV-B causes sunburns and are thought to be linked to skin cancer.
  1. UV-C (200-280 nm) contains the highest amount of energy.
  • Our ozone blocks UV-C. Welding torches, mercury lamps, and sanitizing bulbs can also give off UV-C.

So what is SPF?

SPF stands for sun protection factor. It is the amount of UV radiation required to burn the skin. In other words, it is the length of time someone can spend in the sun without getting sunburn. SPF refers to the amount of UVB protection.

SPF number does not equate to time in minutes! SPF is the amount of UV exposure rather than the time. In other words, wearing SPF 15 would take the sun 15 times longer to burn skin.

The SPF rating and amount of UV-B rays reaching your skin has a marginal relationship.

  • SPF 15: blocks about 93% of UV-B rays
  • SPF 30: blocks about 97% of UV-B rays
  • SPF 50: blocks about 98% of UV-B rays
  • SPF 100: blocks about 99% of UV-B rays

What is PA+?

Remember SPF only refers to UV-B protection. UV-A is slightly more tricky. You might have seen 'PA+++' on Asian sunscreens, or broad-spectrum on US ones. These both refer to a sunscreen providing UV-A protection.

UV-A protection is often labeled by PA+, Boots Stars, or UVAPF.

Unless a company discloses the actual UV-A protection factor, we can only make guesses.

Most UV-A tests look at the amount of time needed to darken skin, or for skin to create melanin. This test is called the Persistent Pigment Darkening method (PPD).

Like SPF, PPD measures the amount of time needed for UV-A to darken skin. This means a PPD or UVAPF factor of 2 means you can be exposed for twice as long before skin darkening.

PA+ is a system in which more plus signs means higher UV-A protection. This is primarily used in Asia, such as Japan and South Korea.

UVAPF/PPD to PA guide: 2 - 4: PA+ 4 - 8: PA++ 8 - 16 PA+++, or 16 or more: PA++++

Click here to learn all about UV-A.


In the US, the FDA considers a broad-spectrum sunscreen to:

  • provide 90% of average UV protection in the 290 to 400 nm range
  • the average of all wavelength protection to be at 370 nm, which is in the UV-A range

In Australia and New Zealand, broad-spectrum encompasses everything above and:

  • The UVAPF to SPF ratio must be 1/3
  • This means a sunscreen with SPF 60 must have UVAPF of 20

Sun protection by location, activity, and time of day

The amount of SPF needed depends on your skin type, your location, your sun exposure, and the time of day.

Skin Complexion

Fair skin tends to absorb more UV than darker complexions. People with a high risk of skin cancer, anyone with albinism, or anyone with an autoimmune disorder should opt for higher SPF ratings and UVA protection.

Location and Time of Day

The amount of UV around you depends on your location and time of day. Those living near or at the Equator and those living at high altitudes are exposed to more UV.

Remember: UV is not correlated with temperature! High altitudes have higher UV index but lower temperatures.

UV-B also fluctuates throughout the day and peaks in the afternoon. According to the FDA, these times may expose you to the same amount of UV: one hour at 9 am and 15 minutes at 1 pm.

UV-A rays remain the same level of strength during daylight hours throughout the year. This means you should still wear broad-spectrum sunscreen in winter!

Although clouds are capable of absorbing some UV, UV rays are still able to get through. Clouds block about 50% of incoming UV.

What is the UV index?

A UV index is helpful to know how strong UV rays are at your location. There are some limitations you should know about.

According to the EPA, UV index takes into consideration both UV-A and UV-B radiation. These indexes are made using a computer model that takes into consideration the ozone, latitude, altitude, cloud cover, day of year, and time of day.

Part of calculating UV index involves looking at wavelength strength and skin response. This is where the UV index gets tricky: because UV-A rays are less powerful in this equation. The equation is also not specific about how it calculates skin response.

However, we know UV-A still causes long term skin damage over time. We also know UV-A doesn't fluctuate as much as UV-B throughout the year.

Your best bet? Definitely wear broad-spectrum sunscreen year-round, no matter your location or UV index.

Should you wear sunscreen when UV index is 0?

Yes! As mentioned previously, a UV index of 0 is a rough estimate of how UV will affect your skin. Many people still tan or burn when skiing or doing winter outdoor activities.

This UV index is from the United States EPA. It is best to take a look into how your country or region derives a UV index to get the full picture.


Spending lots of time outdoors exposes your skin to more UV radiation. Some examples include hiking, skiing, and swimming outdoors.

Damage from UV exposure is cumulative. This means your risk of skin-cancer only increases over time.

It is best to wear broad-spectrum sunscreen with high levels of UVB and UVA protection when outdoors.

How much SPF is good for me?

This depends on the above factors! While SPF 30 is most commonly recommended, it is always best to speak with a professional about the amount you need. A professional will know your location, lifestyle, and skin type to best advise you.

Remember to look for a sunscreen that also provides UVA protection. Keep an eye out for labels such as 'PA+++' or 'broad-spectrum'.

Applying and Reapplying

Remember, SPF does not correlate to time! It is best to reapply sun protection every two hours. If you are sweating or swimming, re-apply more frequently.

Dermatologists recommend ½ a teaspoon of sunscreen for your face, and one ounce of sunscreen for your body.

Be sure to cover everything!


What does sweat/water resistant mean?

No sunscreen is truly waterproof or sweatproof. The time listed indicates the amount of time a sunscreen is effective in water. However, sunscreen should be re-applied as soon you dry off or stop sweating.

What does 'broad spectrum' mean?

Broad spectrum means your sunscreen has both UV-A and UV-B protection. As we mentioned before, SPF refers to UV-B protection. It is best to look for a sunscreen that protects against both UVA and UVB.

The term 'broad spectrum' will vary by country depending on regulations for sunscreen testing. However, all countries require broad-spectrum sunscreen to provide some UV-A protection.


Prolonged exposure to the sun is harmful for the skin. Wearing sunscreen does not stop your skin from tanning but prolongs the time needed to tan. Even wearing a high SPF will not stop your skin from tanning.

Contrary to popular belief, tanning does not protect your skin from the sun. According to skincancer.org, every tan increases your risk of skin cancer.

Finding your sunscreen

Check out over 1,000 sunscreens. You can use filters to find the perfect sunscreen for your skin type, ingredient preference, and more.

Further Learning

If you want to learn about popular sunscreen ingredients, we have a guide for that too! Sunscreen ingredients can be classified into two types and affect the skin differently.

Learn why American sunscreens are lacking. (Hint: it has to do with UV-A protection!)