What is the risk of transmitting STDs (other than crabs) via towels? Background here is: I'm a man. Two years ago, I had unprotected anal sex with another man (giving and receiving). I later freaked out about the STD risk and got tested (at the correct times based on windows for each kind of test) for everything that the local testing center said I could be at risk for: Hep B, Herpes, Syphilis, HIV, Gonnorhea/Chlamydia, and Hep. C (even though they said I was not at risk for that)- negative results for everything. But later, I started reading on the internet about how Trichonomiasis is apparently sometimes transmitted through anal sex. Most importantly, there seemed to be some disagreement online about whether Trich could be spread from sharing bath towels. My current roommate has the habit of sharing bath towels, and sometimes using mine. I never thought about why some people care about the whole business of designating specific towels for different folks living together- always figured it was mostly about avoiding the discomfort and visceral gross-factor of stepping out of the shower and drying off with a damp towel someone else recently used. But is there any legit, health-based reason to avoid sharing bath towels, and is there a risk of spreading Trich (or any of the other stuff) with a towel? In case I expose myself to Trich in the future (I’m bisexual), should I make a habit of not sharing bath towels with other people? Main punchline: is there some legit avoiding-possibly-dangerous-diseases reason to not share towels, or is this just another American ewww-cooties overblown hygiene obsession? [I mention trich, because what I’ve gathered from reading relatively credible sites so far is that there’s no ambiguity about the other STDs and towels, and that crabs/scabies or yeast can get spread that way but aren’t dangerous (I have had a couple penile yeast infections since the unprotected sex encounter.)].

Welcome to the Forum.  I'll try to help.  Most experts recommend against sharing towels because of the THEORETICAL risk of transmitting STIs if present.  The topic has not been studied however and there are equally good (and perhaps better) theoretical reason why it is unlikely that STIs would be spread from one person to another on a towel.  The reasons spread of infection is unlikely include:

1.  The organisms which cause STIs are vulnerable to dying in the environment upon exposure to the air and temperatures lower than body temperature.  The longer the interval since the organisms get onto the material, the more likely they are to become non-infectious or die.

2.  If they get onto moist material, the organisms which cause STIs are more likely to stick to the material than to come off on contact with another person's skin. 

3.  To cause infection, the bacteria present on the contaminated towel would need to come into direct contact with a mucosal surface such as the penile urethra, the inside of the rectum or the vagina. 

Thus while theoretically possible, the risk of transmitting, or having transmitted an STI on a towel which had been used earlier by a person with an STI (including trichomoniasis) is incredibly low and not something I would worry about.  I hope you find this statement is helpful to you.  EWH