Overall, replacing your hairbrush about every six to 12 months is a good baseline for most value-priced brushes; higher quality ones can last years with proper care. That said, the actual length of time they last will depend on other factors such as your hair type, the type of brush and how often you clean them.
You might not think using the incorrect brush for your hair type affects the life of the brush, but it can. Those with thick or curly hair may see wear sooner than others.
An old, dirty or otherwise broken-down brush isn't just unattractive on your countertop, it can actually cause a few issues beyond aesthetics. Gerard Cunningham, a retired cosmetologist and master colorist from Atlanta, says an old hairbrush can contribute to split ends and hair breakage. And bristles with oily buildup can make your just-washed hair look lackluster and weighed-down.
Perhaps more concerning is that a poorly maintained hairbrush can hide mold, yeast and bacteria. Eww! Those are NOT natural ingredients you want on your head. Brushing with that means you're basically just putting the ick you washed out right back onto your hair and scalp, which can further exacerbate issues like dandruff or cause redness and itching.