Cod I buy good brushes and wash them regularly in the childrens top to toe wash - they last for years.
When you say its under your eyes I had a weird similar thing where my eyelashes under my eyes itched and eventually fell out and the ones above went a bit wayward. I try every new mascara that comes out so I assume one of them was the culprit. The lashes are growing back slowly now.
Are you sure its not pollen related I spoke to the pharmacist and she said lots of people are suffering for the first time this year.