There is a widely spread maxim in the skin care industry. Sunscreen is the last step of skin care and the first step of anti-aging. This article will unveil the ultimate meaning of sun protection, allowing you to truly understand the meanings of these two indicators and build a scientific protective wall for your skin.
1. Ultraviolet Radiation: An Invisible Skin Killer
Before delving into SPF and PA, we first need to understand what we are actually preventing. The ultraviolet rays in sunlight are mainly divided into two types based on their wavelengths: UVA and UVB. They are like two different killers with distinct personalities, causing vastly different damage to the skin.
1.1 UVB: The Culprit of Sunburn And Redness
UVB is medium wave ultraviolet light with a wavelength between 290-320 nanometers. It has high energy but weak penetration ability, mainly acting on the epidermal layer of the skin. The damage of UVB is immediate, and the redness, burning, stinging, and even peeling of your skin after being exposed to the summer sun for several hours is the masterpiece of UVB. It can cause skin sunburn, trigger solar dermatitis, and is also an important trigger for basal cell carcinoma and squamous cell carcinoma of the skin. Simply put, UVB is responsible for causing sunburn.
1.2 UVA: The Driving Force Behind Tanning And Aging
UVA is long wave ultraviolet radiation with wavelengths between 320-400 nanometers. Although its energy is lower than UVB, it has extremely strong penetration power and can easily penetrate glass, clouds, and directly reach the dermis layer of the skin. The damage of UVA is cumulative and silent, and you may not immediately feel its presence, but it secretly damages the skin’s collagen and elastic fibers, causing skin sagging, wrinkles, and pigmentation. More importantly, UVA is the main cause of skin darkening, as it stimulates melanocytes to produce a large amount of melanin. Therefore, UVA not only makes you tan, but also ages you. Medically, UVA induced skin aging is known as photoaging, which accounts for over 80% of the causes of skin aging.
2. In Depth Interpretation of SPF
SPF stands for Sun Protection Factor, which is a globally recognized indicator for measuring the ability of sunscreen products to protect against UVB rays. Many people only know that the larger the number after SPF, the better, but they may not truly understand the scientific meaning behind this number.
2.1 How Much UVB Can SPF Block
The value of SPF does not represent the multiple of protection, but rather represents the extension of sun protection time. Its calculation formula is based on the ratio of the time it takes for the skin to turn red from UVB rays with and without sunscreen. A more intuitive understanding is to look at its UVB blocking rate. We can calculate it through a simple formula: SPF 15: can block about 93.3% of UVB.
SPF 30: Can block approximately 96.7% of UVB rays.
SPF 50: Can block about 98% of UVB rays.
SPF 100: Can block about 99% of UVB rays.
2.2 Common Misconceptions About SPF
Misconception 1: SPF values can be stacked. Applying SPF 15 isolation cream and then SPF 20 liquid foundation is not equivalent to having SPF 35 protection. The final sun protection effect is based on the highest value, and sufficient application is key.
Misconception 2: High SPF values can be applied only once a day. No matter how high the SPF value is, sunscreen will fall off due to sweating, friction, and oiling. The correct approach is to reapply every 2-3 hours.
3. PA: The Key to Combating Photoaging
3.1 What Does the “+” Sign in PA Represent?
The number of “+” signs after PA represents the strength of the product’s UVA protection ability. This rating is based on the determination of the PFA value (UVA protection factor), which is the ratio of the dose required for UVA to induce sustained darkening of the skin after using sunscreen to when not in use.
PA+: Effective protection, PFA value is 2-4. It can delay the tanning time of the skin by 2-4 times. Suitable for people who commute daily and have less exposure to sunlight.
PA++: Medium protection, PFA value of 4-8. It can delay the tanning time of the skin by 4-8 times. Suitable for situations where there is a lot of outdoor time.
PA+++: High protection, PFA value is 8-16. It can delay the tanning time of the skin by 8-16 times. Suitable for outdoor activities and seaside vacations in summer.
PA+++: Ultra high protection, PFA value above 16. It can delay the tanning time of the skin by more than 16 times. This is currently the highest protection level on the market, which has excellent effects on preventing photo aging and color spot deposition.
3.2 Do You Know All The Different UVA Logos Worldwide?
In addition to Japan’s PA system, Europe and America also have their own labeling methods for UVA protection. Understanding them can help you purchase sunscreen products from different origins.
EU logo: There will be a UVA symbol on the packaging with a circle drawn around it. This represents the UVA protection provided by the product, which reaches more than one-third of the SPF value and complies with EU standards.
Broad Spectrum: This is the labeling method in the United States. According to the regulations of the US FDA, a product can only be labeled as Broad Spectrum if it has been proven through specific tests that it has a certain degree of protection against UVA and UVB. This means it can effectively protect against UVA and UVB.
4. Sunscreen Practical Guide
4.1 Sunscreen Dosage
Many people complain that they still get tanned after applying sunscreen, and one important reason is insufficient dosage. The determination of SPF and PA is carried out in the laboratory at a standardized dosage of 2 milligrams per square centimeter. To achieve the protective effect indicated on the product label, you must apply this amount.
Facial application amount: For an ordinary person, the amount needed to apply to one face is approximately the size of a coin. If it is a thin texture correction liquid sunscreen, it may require two coins in size.
Whole body application: If you go to the beach, a full body application takes about 30 milliliters (one-third of the capacity of a regular sunscreen bottle).
4.2 Sunscreen Reapplication: The Secret of Timeliness
The chemical components of sunscreen gradually degrade after absorbing ultraviolet light, while the physical components, although stable, may also fall off due to sweating or rubbing. Therefore, repainting is crucial.
Daily commuting: If you spend most of your time indoors without sweating, you can reapply at noon.
Outdoor/Sweating/Swimming: It is recommended to reapply every 2 hours. If you enter the water or sweat heavily, you should immediately reapply after wiping dry on the shore.
How to apply makeup: You can use powder with sunscreen value, air cushion, or sunscreen spray (pay attention to hold your breath and avoid inhalation).
4.3 How to Choose Sunscreen Products for Commuting And Vacation
Commuting scenario: commuting every day, with the main exposure time being 8-9 am and 5-6 pm, and relatively weak UV intensity. Choose products with SPF 30, PA+++, and pay more attention to refreshing and non greasy skin texture, avoiding burden on subsequent base makeup.
Office by the window: If you work by the window, UVA can penetrate glass, so it is recommended to choose PA+++products or close curtains.
Vacation scenario: Long term outdoor activities, especially at the seaside and plateau, with extremely high ultraviolet intensity. High protection products with SPF 50 and PA++++must be selected, and a waterproof and sweat resistant formula must be chosen.