If you experience any eye irritation while wearing eyelash extensions, book an appointment with your local GP or dermatologist, so they can diagnose the problem. If you do have Demodex, Dr. Green claims they're likely to tell you to apply petroleum jelly on your eyelids for two hours, followed by 1-percent permethrin shampoo for 10 minutes, then washing it off, and doing this twice a day. If not, they may prescribe an ointment.
Ultimately, prevention is the best treatment, so keep your lashes clean and, as Dr. Shotter says, "don't be afraid to take a break from extensions every now and then."