Brush Wet HairQ: Should you not brush hair when wet?
A: Generally speaking, it's not a good idea, at least not with a traditional bristle-brush. The more modern "tined" brushes used for blow-dry styling, are acceptable, provided they have widely-spaced tines.
The issue at hand is that wet hair is much more fragile and susceptible to damage than dry hair. Fine-toothed combs and finely-tined brushes (as well as bristled-brushes) all exert a lot of pressure on the wet hair because they either a) try to force the hair between tightly-spaced teeth or tines and/or b) try to direct the hair in multiple directions at once. Wet hair will stretch to the point of misshapenness, and often break off when placed under too much stress.
The best way to detangle and groom wet hair is with a wide-toothed comb. You can use the wide-tooth comb first and then work your way to finer-toothed or tined styling tools.
(Note: While natural bristle brushes are excellent for distributing natural oils and removing dirt from the hair when used to brush dry hair, brushing the hair too much is not good. Over-brushing can lead to split-ends and breakage. Therefore, while you should brush the hair every day, only do so until the hair is smooth and tangle-free.)
Hair combing and brushing basics
How to choose a good hairbrush
How to minimize post-shampoo detangling
Fragile wet hair