Note that you have to use at least SPF50 sunscreen every day, including during winters, including when it’s cloudy (clouds actually don’t reduce UV that much) if you use tretinoin.
The linked sunscreen is SPF 45, which is not suitable if you’re using tretinoin.
(I used tretinoin for five years and it has had a pretty awful effect on my skin- it made it very shiny/oily. It’s unclear how reversible this is. At some point I learned that it’s a side effect of tretinoin and mostly stopped using it. Some people want their skin to look like that and go for tretinoin to achieve it; for me, it looks pretty unnatural/bad and I am very much not unhappy about it.)
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.
The skin is much more susceptible to sun damage. Epistemic status: heard it’s from a doctor practicing evidence-based medicine, but haven’t looked into the sources myself.
It is true that cloud cover doesn’t reduce UV as much as one might think, certainly. But there is a *huge* difference in UV levels between Winter and Summer in Northern Europe. Appopriate levels of sun-cream cannot plausibly be the same regardless of time of year. Time of day also makes a huge difference; if you’re not going outside within 2-3 hours either side of the zenith (in theory noon; in practice moves up to 2 hours off this depending on exactly where you live, local time zones, and daylight saving), you can mostly forget about sun-cream.
There’s certainly a huge difference in the UV levels between winters and summers. Even during winters, if you go out while the UV index isn’t 0, you should wear sunscreen if you’re on tretinoin. (I’m deferring to a dermatologist and haven’t actually checked the sources though.)
Note that you have to use at least SPF50 sunscreen every day, including during winters, including when it’s cloudy (clouds actually don’t reduce UV that much) if you use tretinoin.
The linked sunscreen is SPF 45, which is not suitable if you’re using tretinoin.
(I used tretinoin for five years and it has had a pretty awful effect on my skin- it made it very shiny/oily. It’s unclear how reversible this is. At some point I learned that it’s a side effect of tretinoin and mostly stopped using it. Some people want their skin to look like that and go for tretinoin to achieve it; for me, it looks pretty unnatural/bad and I am very much not unhappy about it.)
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.
Why is sunscreen more important when using tretinoin? What happens when you don’t?
The skin is much more susceptible to sun damage. Epistemic status: heard it’s from a doctor practicing evidence-based medicine, but haven’t looked into the sources myself.
It is true that cloud cover doesn’t reduce UV as much as one might think, certainly. But there is a *huge* difference in UV levels between Winter and Summer in Northern Europe. Appopriate levels of sun-cream cannot plausibly be the same regardless of time of year. Time of day also makes a huge difference; if you’re not going outside within 2-3 hours either side of the zenith (in theory noon; in practice moves up to 2 hours off this depending on exactly where you live, local time zones, and daylight saving), you can mostly forget about sun-cream.
There’s certainly a huge difference in the UV levels between winters and summers. Even during winters, if you go out while the UV index isn’t 0, you should wear sunscreen if you’re on tretinoin. (I’m deferring to a dermatologist and haven’t actually checked the sources though.)