A typical pastry brush has a wooden or plastic handle with natural or synthetic bristles. Unfortunately, this design can promote the growth of bacteria, especially when a baker works with fat-rich glazes like butter. As a result, the pastry brush should be carefully hand washed after each use, and it should be periodically dipped in a bleach solution to keep it sanitary. To hand wash a pastry brush, massage detergent gently into the bristles and then rinse them thoroughly before shaking out the brush and hanging it to dry so that the bristles do not deform.
If you can find one, a better choice of basting brush is an entirely synthetic brush made from a material like silicone. Pure synthetics can be washed in the dishwasher, which makes them much more sanitary. Many of them are also molded in solid units, which makes them easier to clean and prevents the loss of bristles. Silicone is one of the best materials, since it is highly heat resistant.