Choose sunscreen: In addition to the SPF, why should you pay attention to the PA index?

This is an automatically translated article.

The article was professionally consulted with Specialist Doctor I Le Thi Thu Hang - Dermatologist - Department of Medical Examination & Internal Medicine - Vinmec Hai Phong International General Hospital.
There are two systems used to measure a sunscreen's ability to protect against UV rays, namely SPF (sun protection factor) and PA (protection grade of UVA - index. measure your ability to filter UVA rays.Knowing what SPF and PA are will help you choose the right sunscreen for your needs.

1. What is the PA index of sunscreen?

PA (protection grade of UVA) is an index that measures the ability of a sunscreen to filter UVA rays, published by the Japan Cosmetic Association in 1996. It is an independent UVA protection score system. The PA index means the ability to protect the skin from UVA rays. To determine the PA index, the researchers relied on the continuous skin pigmentation test.
Test performed using UVA radiation to induce long-term tanning of the skin. After that, each person's skin will be analyzed and recorded how long the skin becomes darker, comparing the results between unprotected and protected skin in each level. From there, the Persistent pigment darkening (PPD) results are aggregated and simplified into a measure for the PA index:
If the PPD of a product has a result of 2 - 4, then PA = PA +; If the PPD of a product has a result of 4 - 8, then PA = PA++; If the PPD of a product has a result of 8 - 16, then PA = PA +++; If the product PPD has a result > 16, PA = PA ++++. Finally, application manufacturers give a PA rating on sunscreen labels, which manifests as:
Has UVA protection = PA +; Moderate UVA protection = PA ++; High UVA protection = PA +++; Ultra-high UVA protection = PA++++.

2. Analysis of PA index of sunscreen

Compared to SPF, there are some limitations to the PPD test - persistent pigmentation, in PA ratings are as follows:
PPD values ​​are not standardized in all countries and vary from region to region. area. In general, the more plus signs, the more protection from UVA rays. There is no agreement on how the PA value is obtained because the way it is measured is measuring UVA rays that darken uneven skin. In fact, not all skin turns brown from sun exposure or at the same rate, which means that evaluations are inconsistent. 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 ++++. In 2013, Japanese researchers changed the PA Rating System to bring the new highest protection index to PA++++. Please note, not all countries have upgraded to include PA++++. Some only recognize PA+++ as the highest UVA protection available. There is a lot of confusion about what PA really means. In other words, no one knows how long PA ratings last from person to person in real-world use.

3. Sunscreen's PA to SPF rating

When it comes to sunscreen PA ratings, just remember that PA ranks how effective a sunscreen is in protecting skin from UVA rays. Meanwhile, the sun protection factor (SPF) measures how effective a sunscreen is in protecting the skin from UVB rays. Products with SPF 30 block about 97% of UVB rays. However, in general, the higher the SPF value, the higher the PA value. On average, it takes 10-20 minutes after exposure to the sun for the skin to burn. This means that a product with SPF 15 will keep your skin burning for 15 times longer than no sunscreen, which equates to 150-300 minutes of protection. That's why after a few hours, you need to reapply sunscreen.
Types of UV rays that can be harmful to the skin are:
UVA: UV rays with longer wavelengths and lower energy penetrate deep into the skin and cause long-term damage such as wrinkles. UVB: UV rays with shorter wavelengths and stronger energy attack the surface of the skin and cause immediate damage such as sunburn. In a randomized experiment, the process for determining SPF on sunscreens was similar to that of PAs. The test is based on laboratory preformed human skin and on the continuous pigmented darkening (PPD) test. However, checking the SPF on a sunscreen may seem a bit more scientific as it is easier for the skin to regenerate. It is important that both systems are subjective.

4. In addition to the SPF index, why should you pay attention to the PA index?

Checking the SPF of a product that is advertised as having sun protection for the skin is easier to do, and also more scientific. Although the PA+ factor is more subjective, this indicator is used quite a lot in the Asian market. At this point, the PPD testing is different evidence that they are effective and using a product with a high PA + factor is more effective in protecting the skin when choosing a sunscreen.
Besides, when choosing a sunscreen, you should not only rely on the above 2 indicators, but also learn about the other characteristics of the product. Sunscreen with a light cream texture will provide a smoother texture and better grip on the skin. Some products also have the effect of softening and brightening skin tone, without causing oiliness or water-soluble, contributing to the prevention of skin aging, melasma, brown spots on the skin.
In addition, knowing how to use sunscreen is also important to achieve the best effect. Apply the product evenly on the skin, preferably at least 20 minutes before going out in the sun. Not only that, building a daily sunscreen routine is essential for the best skin protection. At the same time, after bathing or sweating a lot, it is also necessary to reapply sunscreen for better effect.
In short, sunscreen brands can be confusing and confusing for consumers when choosing a sunscreen. Performance indicators are manufacturer-dependent, with SPF only measuring protection from UVB rays, while PA numbers only measure protection from UVA rays. However, it is important to always choose a sunscreen that protects the skin from UVA and UVB rays. Thus, knowing how to choose a sunscreen and use it effectively is one of the secrets to keeping your skin healthy and youthful.

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