9 Surprising Things Your Hands Can Tell You About Your Health

4. Downward-curved nails

Condition: Lung diseases

Nails that curve down and bulging fingertips are signs of a possibly serious health condition involving the lungs.

“The most common association is with lung disease, including lung cancer,” Lipner says, but they may also indicate COPD, tuberculosis or other health issues.

What to do: See a doctor as soon as you notice a change, she advises, since treatment may require speed.

5. Hand tremor

Condition: A neurologic disorder

The two most common — and concerning — causes are Parkinson’s disease and essential tremor, says Mark Hallett, M.D., former chief of the Medical Neurology Branch at the National Institute of Neurological Disorders and Stroke. The difference? With essential tremor, the hands are still when at rest. “People will notice the tremor when they are doing something like handwriting, grabbing a cup or eating with a fork,” says Hallett. With Parkinson’s disease, however, the tremor occurs when the hands are at rest and stops when they’re in motion, though that can change as the disease progresses.

What to do: See a neurologist to get to the bottom of your symptoms. ​A hand tremor is occasionally a sign of other rarer neurological conditions or hyperthyroidism, Hallett notes.

6. Spoon nails

Condition: An iron imbalance

If your fingernails are raised on the sides, creating an indentation, you may have a condition known as koilonychia, or spoon nails. “To test for this, you can put a drop of water on the nail,” says Lipner. “If the water stays on the nail, you’ve made the diagnosis.”

The condition has long been associated with an iron deficiency, but it can also indicate an excess of the mineral, as well as both hyperthyroidism and hypothyroidism. Your doctor may need to run some tests to determine the exact cause of the issue.

What to do: Start by consulting your general practitioner, especially if you’re also experiencing fatigue and anxiety, which can be symptoms of both iron imbalances and thyroid problems. Says Lipner, “If you treat the underlying cause, the spooning usually resolves.”

7. Joints that pop

Condition: Trigger finger

Finger joints that stick or lock, accompanied by a pop or clicking sound, are clues to this common condition, which happens when the tendon that allows a digit to bend gets stuck and can’t glide smoothly in its sheath. The condition, which often occurs in the middle and ring fingers, can be quite painful, says Kaplan.

“Trigger finger usually happens in people who have underlying osteoarthritis due to some overgrowth of the bone irritating the tendon,” he explains.

What to do: Rest, splints, gentle stretching and NSAIDs are helpful in quelling the pain. If these don’t work, your doctor may recommend a steroid injection. Surgery to release the tendon is a last resort.

8. Nail pitting, red-brown lines under nails

Condition: Psoriasis or skin cancer

“Commonly, we see [nail issues] in association with psoriasis as well as psoriatic arthritis,” says Lipner.

While you might expect to see skin problems with psoriasis, sometimes pits in the nails are the condition’s only sign. But they may be accompanied by splinter hemorrhages (red-brown vertical lines under a nail that look like splinters), and the nail may be lifted from the nail bed. Dark streaks under the nails can, in rare instances, indicate skin cancer.

What to do: Consult a dermatologist about the possibility of psoriasis or skin cancer, the latter of which can be deadly if not treated.

9. Dark fingernail streaks

Condition: Skin cancer

Black or brown streaks in a fingernail can be a mole or a sign of infection, but there are more concerning possibilities. Dark streaks can also indicate melanoma, the most dangerous form of skin cancer.

“Nail melanomas are actually quite rare,” says Lipner. “However, they’re important to diagnose early because they can be much more deadly than even skin melanomas.” In addition to the vertical lines, melanomas may also cause the nail to split, bleed or seep pus.

What to do: See your doctor if you notice an issue. And since nail changes can go unnoticed among people who get regular manicures, be sure to give your nails a good look once a month, Lipner adds.