The Claim
"Sunscreen is only necessary when it is sunny or you are outdoors."
The Science
UVA rays, which are responsible for the majority of premature skin aging, photoaging, and increased skin cancer risk, penetrate through clouds and glass. On a cloudy day, up to 80% of UV radiation still reaches the earth's surface. This means your skin is being damaged even when you cannot see or feel the sun.
UVA rays also penetrate standard window glass, which is why dermatologists recommend wearing sunscreen even when spending the day indoors near windows. This is particularly relevant for people who work near windows or drive frequently — cumulative UVA exposure through car windows is a well-documented cause of asymmetric photoaging.
The distinction between UVA and UVB is important here. UVB rays cause sunburn and are partially blocked by clouds and glass. UVA rays cause deeper, more insidious damage — breaking down collagen, causing hyperpigmentation, and increasing cancer risk — and they are present year-round, in all weather conditions. Daily broad-spectrum SPF 30 or higher is considered non-negotiable by virtually every dermatologist.
Beyond sun protection, proactive skin health treatments like LED light therapy have strong research backing for reducing the cumulative effects of UV damage including collagen breakdown and uneven skin tone. Learn more at School of Dermatology's light therapy resource.
Key Takeaway
UVA rays penetrate clouds and glass year round and are the primary cause of premature aging. Daily SPF is necessary regardless of weather or whether you are indoors.
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