Unlike synthetic hairs, natural bristles require a different method of washing if you want to clean them and prolong the life of those boar-bristles. However, when you go a step further from just combing out the hair, dust and grime of accumulated styling products before a plain water soaking, the brush will be fresher and conditioned at the same time.
Using a shampoo to wash boar bristles in is a bad idea, but soaking that brush with some dish detergent is another story. I prefer milder dish detergents for this purpose without anti-bacterial ingredients that could possibly cause damage. Yet, I also found that adding some extra-virgin olive oil along with that dish detergent seems to condition those natural boar hairs as well.
DIY Natural Boar-Bristle Brush Cleaner Recipe
1/2 cup of mild dish detergent
3 tablespoons of extra-virgin olive oil
Before you begin, comb out all the imbedded hair, dust and grime in your brush to prepare it for soaking.
Mix the dish soap and olive oil together in a small basin or container suitable to twirl your brush in to coat all the bristles. You will not be soaking.
Once your bristles received this brief treatment, you will run the brush under warm (not hot) water until bubbles are gone and the water appears clear.
Give the brush a thorough shake to get rid of the water; then, lay it out to dry.
By the next day, your brush will be cleaner with a renewed look to those bristles!