This is why the towels in your bathroom smell

Short answer: A bathroom without ventilation never dries out fully. Towels hanging in damp air start to smell, no matter how clean they were to begin with.

Air the room out after every shower

Ten minutes with the window open or the extractor fan on removes most of the moisture from the air before it can soak into towels and the walls around the shower. Without that airing, the room stays saturated with moisture all day, and every piece of fabric in it struggles to dry fully between uses. See bamboo towels.

Hang spread out, not crumpled

A towel hanging crumpled on a hook does not dry, because air cannot reach the inner layers of the fabric. A bar or a wide hook makes the entire difference between a towel that is dry by the next use and one that stays damp and starts developing a smell. See home homewear in bamboo.

Rotate between several towels

With two towels per person, each one gets a full day to dry properly, instead of being reused while it is still damp from last time. That rotation makes a noticeable difference in a bathroom with poor ventilation, where drying time already takes longer than normal to begin with. See bamboo bedding.

Wash without fabric softener

Fabric softener makes towels less absorbent and significantly extends drying time, because it leaves a film on the fibers that holds onto moisture longer than necessary. That is one of the main causes of odor in towels, even when they are washed regularly and look clean at first glance. See bamboo clothing for women.

How material affects odor

Bamboo viscose absorbs and releases moisture faster than thick cotton, which makes the fabric less prone to the bacteria that cause odor. In a bathroom without much ventilation, choosing the right material can make a real difference to how often towels need washing.

The position of the towel bar

A bar placed near a window or an extractor fan dries towels faster than one tucked into a corner with no airflow. Move the bar if you can, or consider adding an extra hook somewhere with better air circulation in the room.

A humidity meter gives an honest picture

A simple humidity meter shows whether the bathroom actually has a moisture problem, instead of guessing based on a feeling. If humidity stays consistently high, more ventilation or an extractor fan is the most effective long term solution to the problem.

Signs a towel needs replacing

If a towel smells again soon after a wash without softener, the fibers are likely worn out and have lost their ability to dry quickly. At that point neither better ventilation nor more frequent washing helps, and replacing it is the only real solution.

Bathroom size plays a role

A small bathroom with a shower and lots of steam struggles to dry out more than a larger room with better air circulation. Compensate with shorter, more frequent airing instead of one long session, if the room is small and moisture builds up quickly.