Am I all of a sudden allergic to bare essentials after 4 years of use??
It could be the make-up build-up, but don’t rule out the allergies! Allergies change every 7 years or so, so it IS possible that you’ve become allergic to something in BE. Eg. My mom got pollen allergies when she came to the US (When she was 20), and I became allergic to my acne cream one day after using it for a year. As for cleaning your brushes — use a mild shampoo and water to soak and wash it very thoroughly! After you’ve gotten all the residue out, wash it again with clean water once or twice, and pat out the water on the brush/brush handles as well as you can and leave it to dry. (Not in a dark/damp place — bacteria!) Next time you try using your BE, put on a bit on a small part of your skin for a day before you apply it to your whole face, to check if you’re allergic.
