If your brushes are caked in old makeup, oil, and debris, you can use a gentle dish soap to effectively cleanse your bristles. However, make sure you read the ingredient list first: if you use a soap that contains harsh solvents or has a high alcohol content, this can ruin your brushes by loosening the glue that secures your bristles into the handles. To cleanse your brushes (natural and synthetic) properly with peace of mind, you can use a dry makeup brush cleaner, makeup brush cleaner shampoo, or solid makeup brush cleaner that’s specially designed and formulated for this task.