Deep in the depths of your makeup bag, there are some shocking truths that you’d probably rather not know. From that year-old liquid foundation to those unwashed brushes, there's a lot of bacteria building up. And while we’ve been turning a blind eye, it's been multiplying. Big time.“It’s a well-known fact that makeup bags are a breeding ground for bacteria,” explains Dr. Anjali Mahto, consultant dermatologist at the Cadogan Clinic. “Many laboratory-based tests where makeup items have been swabbed have shown the growth of all sorts of different microbes that can cause infection.”Nancy Crossley, makeup artist and founder of Beauty So Clean , adds, “We have done studies with outside labs and on average, 11 out of 25 products tested contained Staphylococcus aureus [a common cause of skin infections and food poisoning], Pseudomonas aeruginosa [which can trigger bloodstream infections and pneumonia], and E. coli.”So how much bacteria could be in YOUR makeup bag? Short answer: probably more than you think. But there’s also a lot you can do about it. Read on to find out how.