Although you may call them a loofah sponge, these long, fibrous bath accessories come from a vegetable source and not a sea creature. The luffa plant, a relative of the cucumber, produces large gourds that leave a durable network of fibers after treating and drying the fruit. The resulting mildly abrasive scrubber exfoliates your skin and enhances surface circulation.
The outermost layer of your skin, the epidermis, naturally sheds dead skin cells. Normal friction removes some of these shed cells, but others remain in place, dulling your complexion or turning it ashy. Exfoliation helps this natural process along, using gentle friction to brush excess skin cells from the surface of your skin. Removing dead skin cells not only improves the look of your skin, it also sweeps away places where bacteria and soil could collect.
Any friction on your skin increases localized blood flow. Capillaries, the tiny blood vessels closest to your skin, naturally expand when stimulated. You've made use of this response if you've tried to warm your hands by rubbing them together to create friction and stimulate blood flow. A loofah has a similar effect, stimulating increased circulation to areas that you scrub with it. Unlike harshly abrasive scrubbers and sponges, a loofah's firm but elastic fibers are round in cross section and are less likely to scratch skin.
Loofahs have been touted as a solution to cellulite deposits, but rubbing any object on the surface of the skin cannot change the structure of the skin's lower layers. Cellulite, the dimpled fat deposits that typically appear on the thighs and hips, is no different from subcutaneous fat elsewhere on the body. Like other types of fat, no amount of surface pressure will permanently change its volume or appearance, although a loofah can improve the condition of the skin over the subcutaneous fat.
Loofahs help keep your skin in good shape, but they can also harbor harmful bacteria in their many tiny holes. Like all plant matter, loofahs are also susceptible to decay if kept constantly wet, so let your loofah air dry between uses. Washing it in a mild bleach solution could extend its useful life, but you should replace your loofah frequently. A clean loofah has a mild strawlike smell; any off-putting odors signify a loofah that needs to be replaced. Avoid using a loofah on any part of your skin with reduced sensation; although the fibers in the gourd are unlikely to scratch your skin, it's safer to use only soft materials on areas with low sensation.