If you store your vitamins and nutritional supplements in areas of your home – like the kitchen or bathroom – you may want to consider finding a new place for them. A new study conducted at Purdue University has found that some pills that are stored in areas of high humidity can lose their effectiveness, even if the lids are on tight.

Researchers studied the effects of a process known as deliquescence, in which humidity causes a water-soluble solid to dissolve, on several different vitamins and health supplements.

If you get some moisture present or ingredients dissolve, they’ll decrease the quality and shelf life of the product and decrease the nutrient delivery," said the study’s lead author, Lisa Mauer. "You can get complete loss of the ingredients. It depends on the conditions. It depends on the formulations. Within a very short time – in a week – you can get complete loss of vitamin C in some products that have deliquesced."

Storing products in dry conditions, below their deliquescence relative humidities, can avoid unwanted ingredient loss, according to researchers.

Liquid or condensation in vitamin containers as well as brown spotting may be signs of nutrient degradation. Researchers suggest discarding any dietary supplement that is showing signs of moisture uptake or browning.