Eyelashes protect our eyes from dirt and debris, as well as contain sebaceous glands at the base that lubricates and protects from dryness and irritation. The lifespan of an average eyelash is three to five months, opposed to the rest of your hair which lasts two to four years. Eyelashes are the thickest hair on the human body. Most people have between 150-250 individual lashes on the top of the eyelid and between 50-100 on the lower lid. Eyelashes grow in uneven rows, 5 to 6 on top and 3 to 5 on the bottom.