Proper storage helps preserve ingredient stability and product freshness. Heat, light and air can cause many actives to lose their properties over time. Storing products in a cool, dry place away from direct sunlight is a general recommendation.
Although many store products in the bathroom, shower humidity and temperature swings may not be ideal for some. Keep products at a cool, stable temperature where possible, and close caps tightly after use to reduce air contact.
Airless packaging helps here: it largely isolates content from air and light, supporting stability and allowing fewer preservatives. Track the period-after-opening (PAO symbol) and mind the expiry date.