Cotton terrycloth holds 25 to 30 times its weight in water, so a towel that feels dry is still humid in its inner fibres. That damp, plus your shed skin and sebum, feeds the bacteria you left on it, and the population doubles every couple of hours on a rack in a warm bathroom. The musty smell is the byproduct of that bloom, not the towel itself. Staphylococcus, E. coli, and Pseudomonas survive in damp cotton for days to months at room temperature ¹.

Wash temperature decides what survives. A 60 °C cycle with a bleach-containing detergent drops Staphylococcus aureus and E. coli on cotton by 99.99% or more. A 30–40 °C cold cycle with plain liquid detergent leaves a viable population behind and can carry it between items in the same drum ², ³. Shared hand towels are the busiest route for one person's bacteria to reach everyone in the home ⁴, and dirty face textiles feed breakouts and folliculitis on skin already on the edge ⁵.

Cold-cycle washing is fine for maintenance between deep cleans, not for towels used by someone with an active infection.

Within a week, the bathroom stops smelling damp between showers. By two to four weeks, jawline and back breakouts that ran on background re-inoculation usually settle, especially if you swap the pillowcase too ⁵, and the body odour that returns an hour after washing fades because your sweat now hits clean skin. Over months the household cycles fewer minor coughs and foot itches, and properly laundered towels hold their loft for years instead of going stiff and musty. When a freshly washed towel smells musty again within a day, the biofilm has worked below the depth your washer reaches ⁶; replace it rather than keep washing.