Nowadays, the recognition of sunburn is an effect of UVB which is one spectrum of the light, also the discovery of UVB-specific DNA mutations leading to establishment of UVB as a complete carcinogen. Additionally, UVA, another light spectrum, is well known for causing skin ageing and skin cancer.
What is the indicator for UVB protection?
Ans: SPF
What does SPF mean?
SPF is the ratio of Minimal erythema dose (MED) causing by UVB on sun protected skin divided by Minimal erythema dose causing by UVB unprotected normal skin
For example of SPF 30, if your skin normally burn after 10 minutes in the sun, the sunscreen would protect your skin from burning for approximately 300 minutes (a factor of 30 times longer). This depends on skin type, intensity of sunlight and amount of sunscreen used. If properly applied, a product with an SPF of 30 would allow 30 times as much time in the sun by attenuating 96.7% of the UV reaching the skin. At the same time, an SPF 50 product would allow 50 times as much exposure with the same result by 98% UV reduction.
What is the indicator for UVA protection of sunscreen?
Ans: it is globally differences between country regions because of the difference of measuring indicator!
- In US, Canada, Australia and New Zealand labeled “Broad spectrum” to indicate that their sunscreen cover UVA spectrum
- In European Union labeled “UVA seal” to reveal the UVA protection.
- In Japan labeled “PA+++” as the UVA protection index.
What does PA+++ mean?
Ans: The PA rating system was adapted from the Persistent Pigment Darkening (PPD) method by Japan, this is the test to determine how long it takes for the skin to tan after UVA exposure. With a PPD rating of 16 should infer an individual to take 16 times as much UVA exposure compared to unprotected skin. Because of no standardized system for evaluating PPD score, PPD results are grouped and simplified into PA measurements.
- PPD = 2 to 4, PA = PA+ = Some UVA protection
- PPD = 4 to 8, PA = PA++ = Moderate UVA protection
- PPD = 8 to 16, PA = PA+++ = High UVA protection.
- PPD = 16 or higher, PA = PA++++ =Extremely High UVA protection.
How to choose sunscreen if need to swim in the daylight?
Ans: Choose the product that Lebel water resistant (40) or water resistant (80)
What does water resistant (40) or water resistant (80) mean?
Ans:
- Water resistant (40)=2 × 20-min water immersions (whirlpool bath)
It means that the sunscreen will stay on wet skin for 20 minutes under whirlpool bath for 2 sessions, thus, totally 40 minutes and need air drying in between immersions sessions.
- Water resistant (80): 4 × 20-min water immersions (whirlpool bath)
It means that the sunscreen will stay on wet skin for 20 minutes under whirlpool bath for 4 sessions, thus, totally 80 minutes and need air drying in between immersions sessions.
The American Academy of Dermatology recommends regular sunscreen use with an SPF of 30 or higher for people of all skin types.
Health Canada does not recommend the use of sunscreen for children younger than 6 months because of the theoretical risk of increased absorption of sunscreen ingredients as a result of higher body surface-to-volume ratios and thinner epidermis
What is an adequate amount to apply sunscreen?
Ans: Use estimately 1-2 ounces of sunscreen to cover exposed skin, explain separately in the figure below.
Example: 1 tsp for head and neck, 1 tsp for each arm and 2 tsp for trunk
Reference: Sander M, Sander M, Burbidge T, Beecker J. The efficacy and safety of sunscreen use for the prevention of skin cancer. CMAJ. 2020;192(50): E1802-E1808. doi:10.1503/cmaj.201085
link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7759112/
