The SkinSort Blog

Everything Sunscreen pt. 3: UV-A, PA++, and UVAPF

Updated: November 15, 2023

Sunscreen is the ultimate last step for skincare lovers. Skincare aficionados know the sun is a huge factor in aging. Though aging is a natural phenomenon, the sun can contribute up 90% of the signs of aging.

Aging from sun exposure can look like:
fine-lines, wrinkles, dark spots, uneven skin tone, and the loss of plumpness.

On top of that, sun exposure is cumulative. Every burn and tan increases your chance of developing skin cancer. According to, 1 in 5 Americans will develop skin cancer before they turn 70.

Finding a right sunscreen can be tricky. And SPF is not the only factor that matters. In fact, SPF only gives you a fraction of protection needed.

Keep reading to learn what you should look for beyond SPF. We'll give you a comprehensive crash course on UV-A.

  • What are UV rays?
  • Should you wear sunscreen in winter?
  • Should you wear sunscreen on cloudy days?
  • What is UV index?
  • What is SPF?
  • How is UV-A measured?
  • PA+++
  • Sunscreen labels to look out for

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:

UV-A (320-400 nm) contains the least amount of energy.

  • They contribute to the majority of tanning, long term skin damage such as wrinkles and hyperpigmentation, and Melanoma.

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 believed to cause skin cancer.

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. Welding torches, mercury lamps, and sanitizing bulbs can also give off UV-C.

UV in winter

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

In winter, UV levels are lower due to the Earth tilting away from the sun. Being in the sun all day can still cause tanning or burning even when the UV index is at 0.

This is why people still burn while doing outdoor winter activities such as skiing.

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

UV-B 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.


It's tempting to skip sunscreen on cloudy days. However, clouds are not blocking all the incoming UV radiation.

Clouds can reduce UV levels by roughly 50%. This is why it is important to wear sunscreen year-round and on rainy days.

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. A computer model calculates the index. This equations looks at 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.

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.

This is highly dependent on your preference. Those who want maximal UV-protection should wear broad-spectrum suncreen year-round, no matter your location or UV index.

Should you wear sunscreen when UV index is 0?

As mentioned previously, a UV index of 0 is a rough estimate of how UV will affect your skin.

The answer is yes if you will be outdoors for a prolonged period of time. 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.

In fact, the American Dermatology Association states many skiers often believe they are wind-burned when it is actually sunburn.


To give a quick recap, 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 UV-B protection.

Sunscreens with only SPF factor are likely to be UV-B protection oriented. This means there might be low, or little, UV-A protection.

To find a sunscreen with UV-A protection, look for the following terms:

  • Broad-spectrum
  • PA ++

Measuring UV-A

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

The bad news: unless a company discloses the UV-A protection factor, we can only make guesses.

UVAPF is a measure of UV-A protection. UVAPF measures the amount of UV radiation passing through a sunscreen.

There are several tests done to find these numbers and the requirements vary all over the world.

There are two methods used to determine UV-A protection:

1) IPD (Intermediate Pigment Darkening) measures the skin's initial response to UV-A exposure. It measures how much UV-A is needed to initiate the darkening, or melanin creation process right away.
2) PPD (Persistent Pigment Darkening) is the skin's response to IPD and usually lasts 1-3 days after sun exposure. This test is designed to test the stability of sunscreen. It can be done in-vivo (on live subjects) or in-vitro (elsewhere).

Both of these methods find results in UVAPF.

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.

The PPD method is the standard for deriving UV-A protection for labels such as 'broad spectrum' and 'PA+'.


UVAPF is the standard measurement for UV-A protection.

A UVAPF factor of 4 means your skin is protected for four times longer from skin darkening.

It is impossible to know a sunscreen's true UVAPF unless a company discloses this information (Along with proof from testing). We can make estimations based on regulations from around the world.

Labeling by country

As mentioned before, labeling will vary by country and region. This is due to different regulations and testing methods.

Keep in mind are the bare-minimum requirements to comply with local regulations. Brands are allowed to submit further and more detailed testing, but are not required by law.

What is broad-spectrum?

Broad-spectrum sunscreen labels can be found in the US, Australia, and New Zealand.


In the US, the FDA uses a test called the wavelength test to determine if a sunscreen meets the requirements. This test is done using a plate and passing UV-A radiation through.

The FDA does not require UV-A testing to be done in-vivo (live subjects). On the other hand, UV-B testing must be done on the backs of human subjects.

A sunscreen can can have the label 'broad spectrum' in the US if:

  • 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

This test is problematic because all we know is that it provides at least a little UV-A protection.

From this label, we cannot know:

  • What is the UVAPF?
  • Does it cover the entire UV-A spectrum?

One study from the Journal of Dermatology found 19/20 US sunscreens to meet US requirements. Of these 20 sunscreens, only 11 met the more stringent EU requirements.

Australia, New Zealand, & Canada

In these three countries, the term 'broad-spectrum' sunscreen from these must:

  • 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
  • The UVAPF to SPF ratio must be 1/3

UV-A testing done in Australia, New Zealand, and Canada is also in-vitro (not a live subject). The sunscreen from these countries is more telling than the US. This is due to its ratio requirements.

We can assume a sunscreen with SPF 60 has at least a UVAPF rating of 20.


In the EU, sunscreens will have a UV-A seal, or a circle with 'UVA' inside.

The EU requires in-vitro test for UV-A and in-vivo testing of UV-B.

Though an in-vivo test can be used, there are ethical constraints to these. The in-vitro method is preferred as stated by regulation.

Sunscreens must meet these requirements:

  • A minimum SPF of 6
  • UV-A to UV-B ratio must be 1 to 3
  • A critical wavelength of 370 nm (similar to the US and Australia)

This means every sunscreen in the EU must provide both UV-A and UV-B protection. Otherwise it cannot be a sunscreen!

We have to mention the great sunscreen ingredients that have been used in the EU for decades. These ingredients are still pending approval in the US. These include Tinosorb S and Ethylhexyl Triazone.

What are Boots Stars?

This UV-A protection rating comes from Boots, the UK-based health company.

A sunscreen is given a number of stars based on the UV-B/UV-A ratio over time. It takes into consideration UV-B/UV-A at the time of application vs. after UV exposure.

Due to the requirement of UV-B to UV-A ratio, products cannot technically have less than 3 stars.

Boots sunscreen star ratings
If a sunscreen has a high SPF and 5 stars, you can be sure the UV-B and UV-A ratings are almost 1:1.

For instance, an SPF 60 sunscreen with 5 stars will have UVAPF of at least 54.

What is PA+?

PA+ is a system used in Japan, Korea, and other Asian countries to display UV-A protection. In 2022, it was revised to require in-vivo testing. These tests use the backs of humans to assess darkening after UV-A exposure.

PA+ is calculated by the PPD method. It is a system in which more plus signs means higher UV-A protection.

Here is a UVAPF to PA conversion guide:
2 to less than 4 PA+
4 to less than 8 PA++
8 to less than 16 PA+++ 16 or more PA++++

As you can see, any UVAPF rating higher than 16 will be labeled as PA++++.

In studies, PA is classified like so:

  • PA+ = low protection, 2-4 UV-A filters
  • PA++ = moderate protection, containing 4- 8 sunscreen agents
  • PA+++ & PA++++ high protection, composed of more than 8 UV-A filters


Now you know why it's so important to find sunscreen with broad-spectrum , UVAPF, or PA+ protection. Many sunscreens on the market only protect us from UV-B with minimum UV-A protection. In fact, UV-A protection is important but overlooked in the US.

Getting full protection means finding broad-spectrum, PA+, and UVAPF ratings. The regulations in each country can make these labels mean vastly different things.

Further Learning

To learn all about sunscreen, check out these articles.