TL;DR: Mildew stink comes from bacteria. Standard bath towels are bulky so I kept postponing laundry; switching to compact bath towels (about 50×100 cm) made it easy to wash every few days and stopped the stink and mold.

There’s been a “how often do you wash bath towels?” thread in Japanese forums for decades. The oldest I found was posted 2001/04/08 on a Canada expat board, where replies ranged from weekly to once every two weeks, with a few daily washers. Because it was about life abroad I can’t tell if the longer cycles were climate or culture. On Japan’s OKWave the earliest question was also in 2001, and most answers were “daily or every other day,” so the topic seems to have bubbled up in the late 2000s. As a Japanese person writing from Japan: growing up my mom washed towels every two or three days; now with my own family I wash when I sense a whiff coming—sometimes I stretch it to five days.

Bacteria and that rag smell

Even right after a bath, you still have normal skin bacteria, and the air carries spores and dust. Leave a damp towel hanging and it becomes a petri dish. Rainy-season indoor drying is the classic example: towels turn musty even before you touch them.

Big towels are a pain to launder

Bath towels are huge compared to face towels, and many are thick for absorbency. In a four-person household, washing daily could fill half of a 7 kg machine with towels alone. If rain piles up the laundry, you also run out of drying space. Washing bath towels felt like an “event,” so I kept pushing it back until the smell was unavoidable.

Discovering compact bath towels

Most of us don’t use the full length of a big towel, and I don’t have especially long hair. After a few years of tolerating stinky towels, I spotted Muji’s “compact bath towel” in-store. Regular towels are around 70×140 cm; these are about 50×100 cm.

Muji search: コンパクトバスタオル

If you want something flashier than Muji, search “ミニバスタオル” on Amazon Japan and you’ll get options:

They’re noticeably smaller than standard bath towels but still bigger than a face towel, so they’re perfectly fine for an adult body. The fabric and absorbency are the same as the regular version. I used mine for a couple of days, hung it to dry, and nothing felt different—until laundry day.

Lowering the “laundry hurdle”

On the morning of day three I was loading the washer and saw room in the drum. One or two more towels would fit, but not a heavy full-size bath towel. Then I remembered: my towel is tiny now! In it went.

That’s all it took. Because it barely moves the water level or drying rack space, I now wash bath towels every three days without dreading it.

Black mold spots on towels

When I used white bath towels, I eventually saw tiny black dots. They were mold, and even chlorine bleach didn’t erase them. Towels are thick and slow to dry, so if you leave them damp and skin-oil-laden they become a mold incubator. I suspect the rainy season was when mine turned. Bleach will disinfect, but the stain stayed, so I cut that towel up for rags. Compact towels wash faster and dry quicker, so they’re less likely to get moldy in the first place.

Takeaways

• If you’re worried about how often you wash bath towels, try a smaller size first.
• You can also choose microfiber quick-dry bath towels for even faster drying.
• Don’t give mold a chance—wash regularly and spread towels out to dry.

Later I found a super-absorbent, quick-dry towel that swimmers like to use and bought it on the spot:

Faster post-shower drying with a super-absorbent PVA chamois towel

en.shimashimanoneko.com/posts/seam-towel-hair

Extra: How I removed that musty smell

Once a towel develops the damp, musty odor, regular laundry won’t kill it; even “antibacterial” bleach in the wash only worked for a couple of uses. A soak does the trick, but I hesitate to soak colorful patterned towels in bleach.

A hot-water soak fixes it

Soap scum that survives normal washing can hold odor. Boiling helps melt it off more than it “disinfects.”

“Boiling wash” in a giant stockpot would work, but I don’t own one big enough for a bath towel. Instead, I boil about 2 L of water in a kettle, put the towel in a plastic wash tub, pour the boiling water over it, then top up with hot tap water until the towel is submerged. I press and stir it with a stick or shampoo bottle and leave it until the water cools.

Most of the smell disappears with just hot water. If you want more degreasing power, add washing soda (sesqui). Once the water cools, launder and dry as usual—so much fresher.