Thin eyelashes can be caused by anything from aging and heredity to poor diet. Many believe that castor oil — which comes from castor seeds and has therapeutic and medicinal benefits when used either internally or externally — may help thicken your eyelashes. There is no scientific evidence to support this claim, but if you have thin eyelashes or lack eyelashes altogether, it is worth a try, as castor oil is nontoxic and won't harm your eyes.
Purchase castor oil from your local health food store. Avoid purchasing castor oil from your grocery store because these castor oils may be solely for industrial use. Look for the words "cold-pressed" or "cold-processed" on the label, which indicates that the product is pure and all-natural.
Lather an old mascara wand with water and baby shampoo to clean off any traces of mascara. Avoid using hand soap because it has detergents that can ruin your brush. Air-dry the mascara wand.
Remove any makeup from your eyes and eyelashes with eye makeup remover just before you go to bed.
Dip your mascara wand into the castor oil and tap it on the bottle to remove any excess oil.
Apply the castor oil to your eyelashes in the same fashion as you apply mascara. Work from the inner to the outer corner and swipe the oil on from the eyelash root to the tip. See that all lashes have a thin coating of the oil. Use a cotton swab to wipe away any excess oil.
Leave the castor oil on your eyelashes overnight and wash it off in the morning with a mild facial wash. Apply your makeup as you normally would. Avoid leaving any oil residue on your lashes as it may cause your eye makeup to bleed.