Many organizations that service people are either not allowed or choose not to accept brushes and combs due to the hygiene issues. In general, any hygiene product that directly touches another person cannot be considered sterile again and cannot be reused by another human. This definitely includes things like cosmetics (lipstick, cover sticks, mascara) and personal hygiene products that directly touch the skin such as deodorant. So, hairbrushes and combs might fall into this category as well.
If your priority is to donate to other people, just give your local homeless shelters a call and ask if they will accept used hairbrushes and combs.
However, many local animal rescue organizations will appreciate hair brushes and combs to use on their animals and there is no issue with reusing them on an animal vs. a human. I spoke with the Lexington Humane Society and they said not only do they definitely accept used brushes and combs, but they rarely get grooming items as donations. It’s something they actually fall short of often times, so they are actually very delighted to receive these things.
It’s always a good idea to give your local charity a call to confirm they accept the items in question. Some organizations may prefer to purchase new or already have a steady source of donations for a specific item.
Most brushes and combs are made at least partly from plastic these days, so it’s just one more thing that will be sitting in the landfill for another 500 years or so. What a great way to keep them out of the landfill and help our furry friends too!