There are two systems used to measure the ability of sunscreen to protect against UV rays: SPF (Sun Protection Factor) and PA (Protection grade of UVA). Let's learn about what SPF and PA are!
1. What is the PA index of sunscreen?
PA is a measure of the ability to filter UVA rays of sunscreen, announced by the Japan Cosmetic Industry Association in 1996. This is an independent UVA protection point system. The PA index signifies the ability to protect the skin from UVA rays. To determine the PA index, researchers relied on continuous measurement tests of skin pigmentation.
The test is conducted by exposing the skin to UVA radiation for a long period of time. Then, each person's skin will be analyzed and recorded the time it becomes darker, comparing the results between unprotected and protected skin at each level. From there, the results of persistent pigment darkening (PPD) are synthesized and simplified into a measure for the PA index:
- If the PPD of a product yields results of 2 - 4, then PA = PA+;
- If the PPD of a product yields results of 4 - 8, then PA = PA++;
- If the PPD of a product yields results of 8 - 16, then PA = PA+++;
- If the PPD of a product yields results > 16, PA = PA++++.
Finally, manufacturers apply the PA rating on sunscreen labels, expressed as:
- Offers protection against UVA rays = PA+;
- Provides moderate protection against UVA rays = PA++;
- Offers high protection against UVA rays = PA+++;
- Offers extremely high protection against UVA rays = PA++++.
2. Analyzing the PA index of sunscreen
Compared to SPF, there are some limitations to PPD testing - persistent pigment darkening, in PA classification as follows:
- PPD values are not standardized in all countries and vary by region. Generally, the more plus signs, the more likely it is to protect against UVA rays.
There is no agreement on how to achieve the PA value because measuring UVA darkening is inconsistent. In practice, not all skin turns brown at the same rate from sun exposure, meaning the evaluation is not consistent.
- It is also difficult to determine the difference in sun protection between PPD 20 and PPD 40, both of which are rated as PA+++ or PA++++. Japanese researchers have changed the PA rating system to introduce the new highest protection level, PA++++. Please note, not all countries have upgraded to include PA++++. Some only recognize PA+++ as the highest UVA protection available.
There is much confusion about the actual meaning of PA ratings. In other words, no one knows how long the PA rating lasts from one person to another in actual use.
3. Comparing PA rating with SPF of sunscreen
When considering what the PA index of sunscreen is, just remember that PA ranks the effectiveness of sunscreen in protecting the skin from UVA rays. Meanwhile, the sun protection factor (SPF) measures the effectiveness of sunscreen in protecting the skin from UVB rays. A product with SPF 30 shields about 97% of UVB rays.
However, generally, the higher the SPF value, the higher the PA value. On average, it takes 10 to 20 minutes after exposure to sunlight for the skin to burn. This means a product with SPF 15 will keep your skin from burning for 15 times longer than without sunscreen, equivalent to 150-300 minutes of protection. That's why after a few hours, you need to reapply sunscreen.
4. Types of UV rays that can harm the skin are:
- UVA: Long-wavelength UV rays with lower energy penetrate deep into the skin and cause long-term damage such as wrinkles.
- UVB: Short-wavelength UV rays with higher energy attack the skin's surface and cause immediate damage such as sunburn.
In randomized trials, the process of determining the SPF index on sunscreen is similar to how the PA index is determined. The test is based on pre-shaped human skin in the laboratory and on the continuous persistent pigment darkening (PPD) test. However, testing the SPF index on sunscreen may seem a bit more scientific because the skin can regenerate more easily. The important thing is that both systems are subjective.
5. Besides SPF, why pay attention to the PA index?
Checking the SPF of a product claimed to be sun-protective for the skin will be easier and more scientific. Although the PA+ factor is more subjective, it is widely used in the Asian market. At this point, the PPD testing process is evidence that they are effective, and using products with a high PA+ factor provides better skin protection when choosing sunscreen.
In addition, when choosing sunscreen, you should not only rely on these two indices but also learn about other characteristics of the product. Sunscreens with a light cream texture will provide smoother and longer-lasting adherence to the skin. Some products also have moisturizing effects, leaving the skin soft and smooth, brightening the skin tone, without causing oiliness or melting in water, helping prevent skin aging, pigmentation, and brown spots on the skin.
Furthermore, knowing how to use sunscreen is also very important to achieve the best results. You should apply the product evenly to the skin at least 20 minutes before sun exposure. Moreover, it's essential to develop a habit of using sunscreen daily to provide the best protection for your skin. Also, after swimming or sweating a lot, reapply sunscreen for better effectiveness.