How should I store the bottle so the solution stays effective?

Hydrogen peroxide is a chemically unstable compound by nature: it gradually decomposes into water and oxygen, and this process speeds up with heat, light and contamination. A few simple habits help the 100 ml bottle stay usable for longer:

• keep the cap tightly closed between uses — an open bottle loses activity faster;
• store it in a cool, dark place, for example a first-aid box in a cupboard, away from radiators, direct sunlight and the bathroom's heat and humidity swings;
• never dip used cotton pads or swabs back into the bottle, and do not pour unused solution back in — organic particles accelerate decomposition;
• check the expiry date on the packaging and follow the manufacturer's storage instructions printed on the label.

A practical self-check: fresh, active solution foams noticeably on contact with organic material. If a solution that has been stored for a long time barely reacts at all, it has likely lost much of its activity and it is reasonable to replace it. The compact 100 ml size means the bottle is typically used up before this becomes an issue, whether kept at home, taken travelling or brought to the dacha.