What is PA in sunscreen? Revealing the key indicators of UV protection
As summer approaches, sunscreen becomes the focus of consumers' attention. Among the hotly discussed sun protection topics on the Internet recently, "PA value" appears frequently, but many people are still confused about its meaning and importance. This article will provide a detailed analysis of the scientific definition of PA value, protection principles and purchase suggestions, as well as a comparison of popular sunscreen product data in the past 10 days.
1. Definition and classification of PA value
PA (Protection Grade of UVA) is an international standard for measuring the protection ability of sunscreen products against long-wave ultraviolet rays (UVA). It was proposed by the Japan Cosmetic Industry Federation in 1996. Its grading system indicates the strength of protection through the number of "+" symbols:
| PA level | protective effect | Continuous protection time |
|---|---|---|
| PA+ | Effective protection | 2-4 hours |
| PA++ | quite effective | 4-8 hours |
| PA+++ | very effective | more than 8 hours |
| PA++++ | Super protection | More than 16 hours |
2. Comparison of the differences between UVA and UVB
Ultraviolet rays are divided into UVA (320-400nm) and UVB (280-320nm) according to wavelength. The two have completely different effects on the skin:
| Type | Penetrating power | Main hazards | protective markings |
|---|---|---|---|
| UVA | Reachable dermis layer | Photoaging, wrinkles, spots | PA value |
| UVB | active epidermis | Sunburn, redness, swelling, and peeling | SPF value |
3. Comparison of PA values of popular sunscreen products in the past 10 days
Based on the sales data of major e-commerce platforms and the popularity of social media discussions, the following high-profile sunscreen products have been sorted out:
| Product name | PA level | SPF value | price range | Hot search index |
|---|---|---|---|---|
| Anai sun gold bottle | PA++++ | 50+ | 200-250 yuan | ★★★★★ |
| La Roche-Posay Big Brother | PA++++ | 50+ | 150-180 yuan | ★★★★☆ |
| Biore water-based sunscreen | PA+++ | 50 | 80-100 yuan | ★★★☆☆ |
| Nivea UV gel | PA+++ | 35 | 60-80 yuan | ★★★☆☆ |
4. Scientific verification method of PA value
The PA level is measured using the "persistent pigmentation method" (PPD). The specific process includes:
1. Demarcate a test area on the volunteer’s back
2. Use UVA light source
3. Measure the amount of radiation required to produce minimally noticeable pigmentation
4. Calculate the corresponding relationship between protection factor (PPD value) and PA level:
| PPD value range | Corresponds to PA level |
|---|---|
| 2-4 | PA+ |
| 4-8 | PA++ |
| 8-16 | PA+++ |
| ≥16 | PA++++ |
5. Practical suggestions for choosing PA value
1.daily commute: PA++～PA+++ (office work, short time outdoors)
2.outdoor activities: PA++++ (travel, sports, long-term exposure)
3.Sensitive skin options: Physical sunscreen (zinc oxide/titanium dioxide) combined with PA+++ or above
4.Reapply reminder: Even if it is a product with high PA value, it still needs 2-3 hours to reapply after sweating or wiping.
6. Common misunderstandings about PA value
1."The higher the PA value, the greasier it is.": New chemical sunscreens (such as Tinlaisi S) can achieve high protection and freshness
2."There is no need for high PA on cloudy days": UVA’s ability to penetrate clouds reaches more than 80%
3."PA is directly proportional to SPF": The two protection mechanisms are independent, and the logos need to be viewed separately.
Through the systematic analysis of this article, I believe you have a comprehensive understanding of the importance of the PA value of sunscreen. When purchasing, it is recommended to make a comprehensive judgment based on the usage scenario, skin characteristics and product ingredients to achieve the best UV protection effect.
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