How often should underwear be changed? (Most people are wrong)

Hang on to your drawers: it's time to rethink what's important to you, and do it carefully. If you think your favorite old things might still work, think again. Wear, frequent washing and stubborn bacteria make this comfort a hidden risk. Find out when you should bid farewell to long-term companions to take care of your comfort and health.
Do you have a favorite panties that you've had for years, or a favorite brassiere that you don't want to part with? Wrong idea.

Over time, underwear is subjected to:

Repeated washes modify their elasticity and their retention capacity.
Accumulation of bacteria, even after washing, can cause irritation and infections.
Use of the material which becomes less comfortable and less effective.
So when do they really need to be replaced?