Moisture is one of the biggest threats to stored fabric because it sets off several damaging processes at once, even when the amount of dampness seems small. Three core reasons explain why clothes should never be put away moist.
Microbial growth: Damp fabric provides exactly the conditions fungi and bacteria need to multiply: moisture, warmth and an organic surface to feed on. Left long enough in a closed cupboard, this growth appears as dark mildew spots that are extremely difficult, sometimes impossible, to wash out completely.
Chemical weakening of the fibres: Natural fibres such as cotton and silk are broken down slowly by prolonged contact with water through a chemical reaction that loosens the bonds holding the fibre together. Over weeks or months of storage, this leaves the fabric noticeably weaker, so it tears or thins out faster than fabric that was stored bone dry.
Trapped, stale smell: Since moisture prevents air from moving freely through a folded garment, any dampness that remains simply sits there and turns musty rather than evaporating away, so the smell soaks into the fibres and lingers even after the garment is later worn or aired.
Therefore, clothes should not be stored in moist conditions because dampness invites microbial growth, weakens the fabric chemically over time and traps stale odours that are difficult to remove.