When the seasons change, temperature fluctuations can be quite severe, and you may sweat more and your skin may be exposed to cold outside air. All of these factors make for a harsh environment for your skin. Your skin is more susceptible to stress and fatigue when temperatures change after a season has already taken its toll on your skin. Also, your skin can be more sensitive if you are in ill health or (for women) just before menstruation. That means you could have a reaction to a cosmetic product even if you use it regularly.

If you experience any skin reactions when using a cosmetic product, you should stop using it. Otherwise, you could make your symptoms worse.