It is perfectly normal to lose an eyelash here and there; it happens to all of us. Eyelashes can be lost when mascara is applied or when an eyelash curler is used, or they may simply fall out. Generally, a new lash will grow back and replace the fallen one. However, some people lose lashes in clumps and grow lashes at a much slower rate of up to 2 to 4 months. This may be an indication of a more severe problem. Some conditions that can cause sudden loss of eyelashes are an autoimmune disease, alopecia areata, or hypothyroidism. Please consult your doctor if you suspect that you may be experiencing any of these conditions.