The four little words that make the world spin, “I need a manicure!” never ring quite as true as when you glance down at your fingernails and notice that all of the sudden they’re tinged yellow.

Eek! But don't freak out just yet. We caught up with dermatologist Shereene Idriss, M.D. to find out why this happens and how to combat it:

“Unlike the conventional thinking that healthy nails are firm and hard, the reality is that nails are in fact quite porous," says Idriss. So when nail polish, especially darker shades, are applied to the nail, the pigment can be absorbed. "The iron oxides in those polishes become oxidized and result in the temporary yellow-rust like color that will eventually resolve," she says. Thankfully, it's not permanent. To avoid the staining in the future, "Apply a clear base coat prior to using heavily pigmented polishes," Idriss says. "Also, if you are bothered by the yellow stain, take your nail polish off after a week or so, and dare to go bare every once in a while.”

The gym isn't always the best thing for our finger and toenails, Idriss says. "There's definitely a fungus among us, especially when walking barefoot in the locker room. Athlete's foot is a thing, and it's no surprise the name holds true. Fungus and bacteria can cause the nails to turn yellow-green and eventually acquire chalk-like brittleness," she says. If you think you've gotten something from the locker room, Idriss recommends speaking to your dermatologist, because treatment can vary depending on the source of the discoloration.

“Although the exact reason why is unknown, yellow nails are usually seen in those who suffer from chronic lung disease or poor liver function, and long-term smokers (as nails come into contact with the smoke of tobacco)," says Idriss. "Certain vitamin deficiencies such as B-12 and zinc can also lead to nail discoloration over time.”(Dance your way fit with Women's Health High-Intensity Dance Cardio DVD!)

“This is extremely rare and is known as 'yellow-nail syndrome,' says Idriss of the hereditary condition. "It starts in middle age, and is associated with obviously yellow nails of both hands and feet, swelling in the legs, and respiratory signs such as chronic difficulty breathing. If this affects you or someone you know, treating the underlying lung issues and leg swelling is of crucial importance to your health. Your nails may or may not revert back to normal because the changes are due to a genetic mutation.”