Nymph's Hair

Nymph's Hair is left by Nymphs, which can be encountered by Taking a Walk Around the Pond in the Forest.

When you encounter the nymph, you're given two options:

Go with the Flow means having sex with the nymph, which guarantees a nymph hair, but does not lower libido in any way. This improves reputation with the Nymph.

Resist means starting combat with the nymph. If you fail, the Nymph will likely have sex with you anyway, but you won't gain reputation or a nymph hair. If you succeed, you will gain a hair.

Note: you can only get 1 hair per encounter, so you'll probably need to frequent this area to make any amount of potions with the ingredient.