UV Index does shift meaningfully with season due to the sun's changing angle, but the shift is less extreme — and winter UV is less negligible — than most people assume.
Why the sun's angle drives the seasonal shift
In winter, the sun sits lower in the sky even at midday, meaning UV rays travel through more atmosphere and lose more intensity — the same physical mechanism that makes morning and evening UV lower than midday.
Winter UV isn't zero
Even at meaningfully lower winter UV Index values, extended outdoor time (skiing, winter sports) combined with snow reflection can still produce real sunburn risk — 'it's winter' isn't a reliable substitute for checking the actual UV number.
Latitude changes the picture too
Near the equator, seasonal UV variation is much smaller than at higher latitudes — a tropical destination can have meaningfully high UV Index essentially year-round, unlike a temperate-zone location with a sharp summer-winter swing.
Should sunscreen habits change between summer and winter?
The habit of checking actual UV Index rather than assuming by season is the more reliable approach — daily habitual use matters most in summer or at low latitudes, but winter outdoor activities (especially with snow) still warrant real attention, not a blanket skip.