Do you regularly use makeup sponges? Just as kitchen sponges can become a reservoir for bacteria, so can makeup sponges. As part of your routine, make it a point to regularly wash them.
They need to be washed with soap and water, rinsed, and patted dry on a regular basis – more often than you think!
Check out this article on the NY Times with some some helpful hints, and a quote by Dr. Ehrlich: https://www.nytimes.com/wirecutter/blog/how-to-clean-makeup-sponges/