Hair loss during chemotherapy is widely discussed, but changes to the fingernails and toenails often catch people off guard. Nails are produced by rapidly dividing cells in the nail matrix at the base of each nail. Because many chemotherapy drugs target fast-growing tissues, they can affect this process too — which is why nails, like hair and the lining of the mouth, are vulnerable to change.
The changes take many forms. Nails may darken or yellow, develop horizontal ridges (Beau's lines) that can appear in waves matching treatment cycles, or become brittle and split. When the nail separates from the nail bed (onycholysis), it can be painful or invite infection, and in some cases a nail — often a big toenail — is lost entirely. A new nail that grows in ridged, thickened, or seemingly "doubled" is part of that same recovery process.
These effects are more common with certain drug families, but it helps to remember that nails grow slowly. A fingernail takes roughly six months to fully replace itself, and a toenail a year or more. So changes often linger after treatment ends and improve only gradually. In most people, nails eventually return to normal.
Everyday care can ease things. Keep nails short and clean, and moisturize often to reduce cracking. Avoid aggressive cuticle trimming, gel or acrylic nails, and harsh polish removers. Choose well-fitting shoes so toenails are not pressed or bruised. Cooling the hands and feet during an infusion is sometimes tried, but the evidence for it is not yet settled.
Some signs deserve prompt attention. Redness, swelling, warmth, pus, throbbing pain, or fever around a nail may signal infection. During periods when chemotherapy has lowered your white blood cell count, even a small infection can spread quickly, so do not squeeze or pick at the area — contact your care team instead.
This article is for general information and does not replace medical care. Because the degree of nail change and the right response depend on your specific chemotherapy and overall health, please discuss any worrying symptoms with your own medical team.