The linked sunscreen is SPF 45, which is not suitable if you’re using tretinoin.
Unlikely to be advice that can be generalised.
SPF is a measure of the reduction of UVB reaching your skin [1−(1/SPF)]
SPF 30 means 96.7% protection
SPF 45 means 97.8% protection
SPF 50 means 98% protection
SPF 80 means 98.75% protection
→ There isn’t much difference between SPF 45 and SPF 50+.
Tretinoin increases sensitivity to UV light, but the biggest factor is still the underlying sensitivity of individual skin. For some people SPF 30 may be more than enough, for others, SPF 50+ may not be enough for prolonged sun exposure.
Still important to make sure that you’re using broad-spectrum (UVA + UVB) sunscreen, and that you apply it correctly.
(IDK anything about the underlying contingent facts, but:
there’s a large relative difference between .967 and .98; almost half as much distance to 1. If exposure is really bad, this difference could matter.
If there’s a damage repair mechanism with something like a rate of repair, that mechanism can either be overwhelmed or not overwhelmed by incoming damage—it’s an almost discrete threshold.
)
For sure, but that leads to much more individualised advice of the form “If you’re fine to be exposed to sun for up to 2h with SPF 50, you should not expose yourself for much more than 1h with SPF 30”. The quoted section makes it seem like “You’re fine as long as you wear SPF 50+ sunscreen, but SPF 45 just won’t cut it.”, which doesn’t generalise for most individuals and their level of sunlight exposure.
Unlikely to be advice that can be generalised.
SPF is a measure of the reduction of UVB reaching your skin [1−(1/SPF)]
SPF 30 means 96.7% protection
SPF 45 means 97.8% protection
SPF 50 means 98% protection
SPF 80 means 98.75% protection
→ There isn’t much difference between SPF 45 and SPF 50+.
Tretinoin increases sensitivity to UV light, but the biggest factor is still the underlying sensitivity of individual skin. For some people SPF 30 may be more than enough, for others, SPF 50+ may not be enough for prolonged sun exposure.
Still important to make sure that you’re using broad-spectrum (UVA + UVB) sunscreen, and that you apply it correctly.
(IDK anything about the underlying contingent facts, but:
there’s a large relative difference between .967 and .98; almost half as much distance to 1. If exposure is really bad, this difference could matter.
If there’s a damage repair mechanism with something like a rate of repair, that mechanism can either be overwhelmed or not overwhelmed by incoming damage—it’s an almost discrete threshold. )
For sure, but that leads to much more individualised advice of the form “If you’re fine to be exposed to sun for up to 2h with SPF 50, you should not expose yourself for much more than 1h with SPF 30”. The quoted section makes it seem like “You’re fine as long as you wear SPF 50+ sunscreen, but SPF 45 just won’t cut it.”, which doesn’t generalise for most individuals and their level of sunlight exposure.