If you suffer from allergies or hayfever and are prone to rubbing your eyes, you are not a good candidate for synthetic eyelash extensions. People who have sensitive skin all around the eye area when using make up or any sort of skin care may not consider eyelash extensions, although many with sensitive skin find no problems with synthetic eyelash extenders. Those who use eye drops could cause synthetic eyelash extenders to clump up. Very curly eyelashes are not ideal for eyelash extensions as applying glue and the extension is very challenging and the final result will not be the thick, dark lashes that are desired. Consult with your beauty professional if you should have any questions or concerns.