Yes! Even on a cloudy day, there is still enough UV present to activate the SPOT.  Being outside is where you are exposed to damaging UV sun rays and at the most risk of overexposure, sunburn, premature ageing, skin damage and skin cancer. This is why our SPOTs are for EVERYDAY outdoor use! SPOT check and know when to reapply!When it is cloudy outside, the colour change takes longer. Expect to wait 5 minutes.