Most of the time, it's best to avoid thinking too long or hard about what kind of gunk is collecting between the bristles of your hairbrush. A little cheerful denial goes a long way in this case; after all, anything that gets caught in the brush started off on your head. But clearing that stuff out regularly is important for the health and appearance of your hair, so it should be a weekly task. Both your brush and your skin can safely handle some regularly-scheduled cleaning. Sanitizing brushes doesn't require any harsh chemicals.
Using Warm, Soapy Water
Even the most expensive, handmade hairbrushes can be washed with nothing but good, old-fashioned soap and water. This method works even for brushes made with wooden handles or rubber pads (the part of the brush that holds the bristles). But dunking the brush into the water isn't a great idea, as water can seep through the holes in the brush's pad and either damage the brush or give it a smell of mildew. Proceed carefully so that only the bristles get wet.
Washing and Rinsing the Brush
Start the cleaning process by removing any hairs still lingering in the brush's bristles. Pull them out by hand or slide a comb through the bristles to snag the hairs. Squirt a little dishwashing liquid in a bowl and fill it with a few inches of warm water. Holding the brush with the bristles facing down, lower the brush into the water so the bristles are submerged but the handle and the pad is dry.
Swirl the brush a few times and pull it out of the water. Use a clean toothbrush or other soft bristle brush to gently scrub at the base of the bristles, removing any residue still lingering there. Fill a second bowl with warm water only and repeat the dipping and swirling motion to clean off any remaining soap. Get down at eye level with the bowl to make sure that you're getting the base of the bristles into the water without submerging the entire pad. Let the brush air-dry, bristles down.
Cleaning Brushes After Lice
When cleaning brushes after a bout of head lice, start by soaking them for 15 minutes in very hot water. It should kill any nits still hanging around. Alternately, seal brushes in plastic bags and put them in the freezer for at least 24 hours. Follow either step with the soapy water cleaning method.
Running Them Through the Dishwasher
The dishwasher can handle greasy utensils and baked-on food, so it should be up to the task of sanitizing your hairbrush. This method is only appropriate for certain types of brushes, though. A brush made with wood or natural bristles may be damaged by the dishwasher. Brushes made entirely of plastic or ceramic are good to go, though. The same is true of plastic combs.
Clear out any stray hairs and drop the brush into the utensil basket or lay it flat on the dishwasher's top shelf. Run the washer on its usual setting. It's unlikely that a plastic or ceramic brush will be damaged by the dishwasher – but just in case, don't use this method for pricey brushes.