There’s not a big concern, unless one is immunocompromised or has significant skin disease. Actual health risks are otherwise pretty minimal.
My towel? Every couple weeks, I guess. I don’t use a washcloth, and I borrow my wife’s scrubby for my face. With a new baby in the house, I Purel my hands a LOT.
Despite being raised by Qadgop, I reuse towels a LOT. I only have three of them, and my hair is long enough and absorbent enough to soak a towel on its own. And laundry costs money! I wash mine whenever I’m already doing laundry and curse the extra load…
We all have our own towels which are washed every couple of days. Hand towels changed daily. I don’t use anything other than my hands and shower milk to wash myself so no sponges or face washers.
Any guest would definitely get their own clean towel, hand towel, face washer and soap.
As a guest if I was not given a clean towel, (it has never happened) I would ask for one.
I would NEVER use someone else’s wash cloth!
But I don’t have a washer/drier so I use my towels for two weeks or longer before I throw them in the growing pile of laundry on my floor. Don’t even ask about my sheets! Otherwise I never wash my poof but wash the soap out of it in the shower after every use. Bacteria is good for you.
I dilute some shampoo in a bottle, squirt it back there, do a little dance to rub the cheeks together, then bend over and rinse. All done!
I worship the folks at Suave. I use their shampoo for my face and body too. It’s cheap and very versitile. Yay!
I have my own en suite and therefore I’m the only one who uses my towels and facecloths/sponges, I wash them once a week or so. I’ve taken to soaking my facecloths in a bowl of water with disinfectant overnight recently for no particular reason …
I wash our towels about every week and a half, and change them every four days, about. If we had our own washer and dryer I’d do them more often. Laundry is $3.50 a load, so I can’t afford to do it every day. 
I don’t use scrubby things, just lots of soap.
Towels get replaced once a week or when they start to smell, whichever comes first. We each have our own, plus drop another one on the floor to soak up any excess sprayage. Neither of us use a washcloth or a scrubby.
I set out a fresh towel and washcloth for each guest, plus have a supply in the closet for them if they need more. I’d never dream of asking them to share.
I wash my towels once a week. If they’re the white towels, they get bleached. The scrubby-poofy thing gets bleached weekly also.
I used to wash my towels after two or three uses, but my parents yelled at me for using so much water. I’ve just smelled the towels that have dried me all week, along with my son and his mother this morning, and they smell fine. I’ve smelled smelly towels and these aren’t. They’ll get washed tomorrow, but seeing as I haven’t had a staph infection in years, I’m in no hurry. And I thought I was a germophobe.
Clean wash cloth every time, but that’s because I have dozens.
Towels (every one has their own, and if I find mine damp I leave it on the offender’s bed) get washed when the bathroom gets cleaned, when there is room in the wash, or when I can not remember that last time I washed towels.
I have never noticed a towel smelling nasty.
I dry my face with my hair towel, wrap my hair, and the use the body towel.
I have a washcloth for my face, a towel for face & hair and a towel for my body. I use either my hands and soap, or a scrubby and shower gel in the bath.
I wash towels about once a week, whenever I wash the rest of the clothes.
My husband and I share towels, but I don’t expect our guests to share towels or washcloths with us.
My daughter has her own towel, but that’s because she’s a baby and she has the cute hooded towel. 
Related question! I always wash my towels in hot water. IMO, a towel that cannot stand up to hot washing is no good. It’s unhygenic to wash them in tepid warm water. So, of course, our towels have gone from a pretty soft green to an icky yellowy color. Can anyone recommend a brand of towels that does not lose color when washed in hot? Not too expensive, please…
Oh, and I do a load of towels once a week, I have a nice little rotation system, plus the kid’s towels go in with their laundry.
What about plain white towels? They can’t fade and match everything!
Tap water is treated to make it safe for drinking, but AFAIK it’s not chlorinated to such an extent that’s is in itself effective for killing bacteria on your skin.
I use about 2 towels a week. It’s normally very hot and dry here (over 100F today–in mid-autumn!), so towels dry too quickly to allow mildew to accumulate.
Once a week towel-washer here. I only use it for my hair, though, as I just air dry everything else. I don’t know why, but I hate drying off. It seems a huge waste of time to me. I know that’s weird, but as weirdnesses go, it isn’t that bad.
Towel load - once per week. One towel per shower.
No washcloths - I use the scrubbies (one for face, different color for the rest of the body [washed separately]). I have a jar of extras in case anyone needs to catch a shower at the house; I love the dollar stores - 4 pack for a buck, and friends take the scrubbies, or I just chuck them. Ditto with small wrapped sample toothbrushes - great little pre-thoughts for when one of my friends crashing over has forgetten one.
Side question - Does anyone use or even own hand towels? I used to buy full matching sets of towels (bath & hand & face), but I found I pretty much never used them, they took up lots of space, and for the most part, when I go to someone else’s house, the guest towels are those really pretty embroidered ones that look like they are more for looks than actual use. (Don’t worry, I do wash my hands, but I dry them on toilet paper.) Call me weird, but embroidered towels are more for looks than use. I have one set of hand towels for guests.
Aren’t we all conceived and born in the nether regions?
[QUOTE=Jervoise]
Tap water is treated to make it safe for drinking, but AFAIK it’s not chlorinated to such an extent that’s is in itself effective for killing bacteria on your skin.
QUOTE]
When I fill the tub for a bath, the water is the same level of blue as a swimming pool. Overly high doses of chlorination in treated water is one of the reasons tap water isnt good to drink if I recall my information correctly. It makes me ill to drink it either way. This is the city of Chicago tho, and other places I have lived do not chlorinate at the same level. Either way, my suggestion that the chlorination of the water was doing some work on bacteria was half in jest of this high level and half out of curiosity as to whether it made a difference at all.
[slight hijack] 
Life cycle of my towels:
Climb out of dryer
Hang on towel rack for a while (kind of boring)
Dry off the primate
Stretch out on the bed for the ape to sit on
Hang on a hook in the bedroom for 24 hours
Climb on top of the oil heater (suspenseful)
Sit rolled up on a table beside the bathtub for a few minutes
Dry the primate again
Stretch out on the bedroom floor for the ape’s feet to rest on
Jump into the laundry basket two days later
Swim with my friends
Tumble with my buddies
Washcloths: I use two each shower: one for washing and one for rinsing.
Guests, hmm, well, I just realized I don’t do anything for them. I just assume that they’ll use a clean towel each day from the stack in the bathroom, and use however many washcloths they want to use, and that they’ll toss them into the laundry when done. Guess it would be better manners if I specified, eh?
Hey, those of you who “soap only” (no washcloth or scrubby): how do you get clean? I thought the scrubbing action actually did more cleaning than the chemical action of the soap.
hm, disposable single use buff puffs on face, scrubby gloves on body, resoaped and washed out after shower every day and hung to dry, chlorinated soak once a week.
I use a turbie towel on my face, then to wrap my hair and head in, and i have a terrycloth khaftan that I shinny into to absorb random surface water while i walk around getting my clean clothes out for the day. The turbie and khaftan get washed about every third day. i actually have a couple turbies and khaftans…so it is sort of on on and one in the wash at any given time. I have a third turbie and khaftan at my boyfriends flat in germany. Husband uses the same towel for everything and it gets washed every third day. We also change the bed linens every third day.