Changing your underwear every day might be crucial in the case of  catching some disease. The thing 
is that the fabric from which the  underwear is made is favorable for the growth and development of  bacteria.
Changing your underwear every day means that you will avoid making room for the following health issues:
- Strong itching in the genital area
- Rash and sores
- Developing a large number of infections
- Urinary tract infections
In order to eliminate the chance these to happen, you should try to  change your underwear every day. After you take your daily shower change  your underwear, or even if you don’t take a shower you should always  change your underwear.