Like pollen, mold can create tiny particles that can pass right through the respiratory tract and enter the bloodstream.
If you’ve recently had a water-damage event, you could have mold or harmful bacteria particles circulating in the air in your home. For many people, exposure to these can produce an allergy-like reaction. That’s why it’s always important to take care of water damage.
If you have water damage, I’d recommend calling your insurance company right away if you have one, (as it may be covered by insurance) and ensuring that someone is there within 24 hours to remove the wet building material. Some molds can grow in as quickly as 24 hours. Once the wet building material is removed, it’s important to make sure the surrounding area stays dry. I recommend dehumidification over air movers (another piece of water-damage equipment), as air movers could unintentionally blow mold and/or toxins around.
If you think the water may have intruded for longer than a 24-hour period, then you will want to hire a professional mold remediation firm to remove the building material under the proper engineering controls (with personal protective equipment, plastic containment, and air scrubbers). Reacting as quickly as possible is the best way to ensure that the problem doesn’t get bigger and cause adverse health reactions from neglecting to dry the space properly within the first 24 hours.
Cleaning up with just a towel is not enough as water can remain trapped between building substrates for longer periods of time, even after the surface itself is dry. (Think about what happens if you leave a wet towel on the floor. The floor underneath the towel stays wet for a long period of time because it traps moisture between the floor and the towel. This is what happens between your walls and floors when there is a substantial leak.)