Comprehensive Guide to Sun Protection Measurements

March 19, 2021

Why do dermatologists usually recommend sunscreens with an SPF of at least 30? Should we always buy sunscreens with the highest SPF? What is the difference between SPF and PA?

While it is common knowledge that using sunscreen is necessary to protect our skin health, the science behind sunscreens and how they work can be tough to understand. To help you make an informed choice about which sunscreens to invest in, we cut through the confusing jargon and share what you need to know about sun protection measurements on your sunscreen packaging.

Sun Protection Factor (SPF)

Sun Protection Factor, or SPF, is the most common measurement that you will find on sun protection products. This value indicates the level of sunburn protection provided by the sunscreen. To determine the SPF value, tests are done to measure the amount of UV exposure it takes to cause sunburn when using a sunscreen compared with how much UV exposure it takes to cause a sunburn when not using one.

As SPF values are determined from a test that measures protection against sunburn caused by UVB radiation, SPF values are only an indication of a sunscreen’s UVB protection. For sunscreens that are labelled “Broad Spectrum SPF”, these products have passed a separate broad spectrum test that can demonstrate that they can provide both UVA and UVB protection.

While it is true that higher SPF values provide greater sunburn protection, various misconceptions about SPF have sprung up over the years. In fact, studies have found that many people are likely to use high-SPF products improperly and expose themselves to more harmful ultraviolet radiation than people who rely on products with lower SPF values.

This can happen for a few reasons. For example, some people believe that SPF relates to time of solar exposure – if they normally get sunburned in one hour, then an SPF 30 sunscreen should allow them to stay in the sun for 30 hours (e.g., 30 times longer) without getting sunburned. This is incorrect, as SPF is directly linked to the amount of UV exposure rather than time, and should not be used to determine duration of exposure.

Some people also assume they get twice as much protection from SPF 100 sunscreen as from SPF 50, but the truth is that the extra protection is not required unless you have very photo-sensitive skin. Properly-applied SPF 50 sunscreen blocks 98 percent of UVB rays; SPF 100 blocks 99 percent. When used correctly, sunscreen with SPF values between 30 and 50 offers adequate sunburn protection, even for people most sensitive to sunburn.

Persistent Pigment Darkening (PPD) and PA

Commonly used in Asian countries like Japan and South Korea, this sun protection measurement system is similar to SPF, with the main difference being that this one measures UVA protection rather than UVB.

Persistent Pigment Darkening (PPD) is an in vitro test conducted on a panel of people exposed to UVA light. They all are analysed on the time it takes for their skin to tan, and then the results are compared between protected and unprotected skin. A PPD of 10 will indicate that it takes around 10 times longer for your skin to tan, compared to if it was unprotected.

PA, or Protection Grade of UVA, is the system that simplifies and groups the ratings of the PPD test:

UVA Protection PPD
PA+ 2-3.9
PA++ 4-7.9
PA+++ 8-15.9
PA++++ 16+


The main limitation of PA is that two sunscreens with a PPD of 20 and a PPD of 50 would both be rated as PA++++, and there’s no way to tell which one offers the higher protection.

Critical Wavelength

In certain sunscreens, such as our Heliocare topical sunscreen range, you may observe the following measurement rating: λc 370nm.

This unfamiliar rating actually refers to the critical wavelength, which is the wavelength where the sunscreen allows 10% of the rays to penetrate. A sunscreen with a critical wavelength over 370nm (indicated by λc 370nm) is considered by the U.S. Food and Drug Administration, which has one of the strictest sunscreen regulations in the world, to provide excellent UVA protection.

Heliocare Topical Sunscreens: Beyond SPF & PA

Now that we have are better informed on how sunscreens are labelled and what the numbers mean, it is easier to understand why simply buying sunscreens based on sun protection measurements is unwise.

Other than having a decent sun protection measurement, it is important to make sure that your sunscreen complies to high quality production standards, is suitable for your skin type, and in line with your skincare professional’s recommendations.

Take Heliocare’s topical sunscreen range as an example – our sunscreens have been acknowledged to have the best full-spectrum coverage in the market, but what truly sets them apart from the crowd is are the superior formulations that are designed with consumers in mind. Each sunscreen is formulated with an optimal combination of high-quality filters that are well-distributed within the products to ensure uniform protection, which is no wonder why Heliocare sunscreens are recommended by over 50,000 dermatologists in over 80 countries.

In addition, there is a wide variety of sunscreens to cater to every skin type and skin problem. Have skin dehydrated by photoaging and need a moisturising sunscreen? You will love the Heliocare 360º Water Gel SPF 50+ that provides long-lasting hydration. Need a sunscreen that controls your sebum production? Check out our customer-favourite 360° Gel Oil-free SPF 50. No matter what your skin need is, Heliocare definitely has a topical sunscreen that fits the bill.

Ready to find a Heliocare sunscreen that works for you but don’t know what’s best? Feel free to drop us an email at enquiry@heliocare.com.sg!

Purchasing Heliocare from unauthorised sources could lead to health risk and complications. Buy only from authorised clinics, websites, and stores. If you’re unsure of the authenticity of your Heliocare products, please contact us and we’ll be happy to advise.