The Sun Care Glossary: SPF, PA, UVA, UVB, and More
TL;DR
- SPF measures UVB protection, while PA ratings and "Broad Spectrum" indicate UVA protection
- Understanding terms like photostability and water resistance helps you choose effective products
- This glossary covers both common and technical terms you'll encounter when researching sun care
Sun care comes with its own vocabulary. Labels are covered with abbreviations, products make claims using technical terms, and articles throw around jargon that can leave you more confused than informed.
This comprehensive glossary breaks down every sun care term you're likely to encounter, from the basics to the more technical. Bookmark this page for reference whenever you're researching sun protection.
The Essentials
SPF (Sun Protection Factor) The most recognized sunscreen metric. SPF measures protection against UVB rays—the primary cause of sunburn. The number indicates how much longer you can stay in the sun before burning compared to unprotected skin.
SPF 15 blocks approximately 93% of UVB rays, SPF 30 blocks about 97%, and SPF 50 blocks about 98%. Higher numbers offer diminishing returns. These percentages only apply when you use the recommended 2mg per square centimeter.
UVA (Ultraviolet A) Longer wavelength UV rays (320-400nm) that penetrate deep into the skin's dermis. UVA rays are present throughout the day, penetrate clouds and windows, and are primarily responsible for premature aging (wrinkles, dark spots) and contribute to skin cancer risk. UVA intensity is relatively constant throughout the year.
UVB (Ultraviolet B) Shorter wavelength UV rays (290-320nm) that affect the outer layers of skin. UVB rays are the primary cause of sunburn and play a significant role in developing skin cancer. UVB intensity varies by season, time of day, and location.
Broad Spectrum A regulatory term in the United States indicating that a sunscreen protects against both UVA and UVB rays. To carry this label, the product must pass a critical wavelength test showing meaningful UVA protection. Always look for this term—SPF alone only measures UVB protection.
Protection Ratings
PA (Protection Grade of UVA) A rating system developed in Japan that indicates the level of UVA protection. Ranges from PA+ (some protection) to PA++++ (extremely high protection). Based on the PPD testing method. Common on Asian sunscreens and increasingly seen on international products.
PPD (Persistent Pigment Darkening) A testing method for UVA protection that measures how much UVA exposure is needed to produce persistent tanning compared to unprotected skin. A PPD of 10 means you can receive 10 times more UVA before tanning. European and Asian products often list PPD ratings.
UVA-PF (UVA Protection Factor) Similar to PPD, this metric measures UVA protection. European regulations require that UVA-PF be at least one-third of the labeled SPF for a product to display the UVA seal (a circle around "UVA").
Critical Wavelength A measurement used in broad spectrum testing. It indicates the wavelength below which 90% of the sunscreen's absorption occurs. A critical wavelength of 370nm or higher indicates broad-spectrum protection. This is the basis for the FDA's broad spectrum designation.
Ingredient Categories
Mineral Sunscreen (Physical Sunscreen) Sunscreens using zinc oxide and/or titanium dioxide as active ingredients. These minerals sit on the skin's surface and physically block and scatter UV rays. Generally considered gentle and are recommended for sensitive skin and during pregnancy.
Chemical Sunscreen (Organic Sunscreen) Sunscreens using carbon-based compounds (like avobenzone, homosalate, octinoxate) that absorb UV rays and convert them to heat. These absorb into the skin rather than sitting on top. The term "organic" here refers to carbon chemistry, not farming practices.
Hybrid Sunscreen Sunscreens that combine both mineral and chemical filters to leverage the benefits of each type.
Key Ingredient Terms
Zinc Oxide A mineral UV filter that provides broad-spectrum protection against both UVA and UVB. Known for being gentle and having anti-inflammatory properties. May leave a white cast, especially in higher concentrations.
Titanium Dioxide A mineral UV filter primarily effective against UVB with some UVA protection. Often used in combination with zinc oxide for broader protection. Tends to create a white cast, though micronized versions reduce this.
Avobenzone A chemical filter that provides excellent UVA protection. Known for being unstable when exposed to sunlight unless combined with stabilizing ingredients like octocrylene.
Photostability The ability of sunscreen ingredients to remain effective after exposure to UV light. Some ingredients degrade when exposed to sunlight, reducing protection over time. Modern formulations typically include stabilizers to maintain protection.
Performance Terms
Water Resistant An FDA-regulated term indicating the sunscreen maintains its SPF level after a specific duration in water: either 40 minutes or 80 minutes. The time must be stated on the label. No sunscreen is "waterproof"—this term is banned by the FDA.
Very Water Resistant In some markets, this indicates 80 minutes of water resistance (the maximum testable duration). Check the specific time listed on your product's label.
Sweat Resistant Though sometimes used in marketing, this is not an FDA-regulated term. Water resistance testing simulates water exposure but doesn't specifically test sweat conditions.
Regulatory Terms
GRASE (Generally Recognized as Safe and Effective) An FDA classification for drug ingredients. Currently, only zinc oxide and titanium dioxide are classified as GRASE for use in sunscreens in the United States. Other ingredients are still under review and can still be used, but haven't received this formal status.
Active Ingredients The components in sunscreen that actually filter UV rays. In the US, these must be listed in a standardized "Drug Facts" box on the label with their exact percentages.
Inactive Ingredients All other ingredients in the formula—emollients, preservatives, fragrances, stabilizers. These don't filter UV rays but affect product texture, stability, and feel.
Specialized Terms
UPF (Ultraviolet Protection Factor) The SPF equivalent for fabrics and clothing. Indicates how much UV radiation can penetrate the fabric. UPF 50 means only 1/50th (2%) of UV rays pass through. Look for this rating when purchasing sun-protective clothing.
HEVL (High-Energy Visible Light) Also called blue light or visible light (400-500nm). Some research suggests HEVL may contribute to hyperpigmentation and photoaging. Iron oxides (common in tinted sunscreens) help protect against visible light.
Infrared (IR) Radiation beyond visible light that produces heat. Some premium sunscreens claim IR protection, though the clinical significance is debated.
Antioxidants Ingredients like vitamins C and E that help neutralize free radicals generated by UV exposure. Often included in sunscreens as a second line of defense beyond UV filtering.
Application Terms
Teaspoon Rule A guideline for facial sunscreen application: approximately 1/4 to 1/2 teaspoon for face and neck. This helps achieve the protection level indicated by the SPF.
Two-Finger Rule Another application guideline: squeeze sunscreen along the length of your index and middle fingers for adequate facial coverage.
Shot Glass Rule The amount of sunscreen (approximately one ounce or 30ml) needed to cover an adult's entire body in a swimsuit.
Key Takeaways
- SPF measures only UVB protection; look for "Broad Spectrum" or PA ratings for UVA coverage
- Mineral and chemical sunscreens work differently but both provide effective protection
- Water resistance is tested at 40 or 80 minutes—always check and reapply accordingly
- Understanding these terms helps you make informed choices about sun protection products
FAQ
Q: What's the difference between "sunscreen" and "sunblock"? A: These terms used to distinguish between chemical (sunscreen) and physical (sunblock) formulas. However, the FDA now only permits the term "sunscreen" on labels. "Sunblock" implied complete blocking of UV rays, which no product achieves.
Q: Why don't US sunscreens have PA ratings like Asian products? A: Different regions use different testing and labeling systems. The US uses "Broad Spectrum" to indicate UVA protection, while Asian countries use the PA system based on PPD testing. Both indicate UVA protection but use different scales and terminology.
Q: What does "non-nano" mean on mineral sunscreen labels? A: "Non-nano" means the zinc oxide or titanium dioxide particles are larger than 100 nanometers. There has been some concern about whether nano-sized particles could penetrate skin, though current research suggests they stay on the surface. Non-nano products may have more visible white cast.
