When most of us look at our hands, we might notice that we need to trim, clean, or stop biting our fingernails, and that's about it.

But if you ask a dermatologist, they can see a whole lot more. Everything from poor diet and stress to serious kidney problems can be revealed by a glance at your fingernails.

There are about 30 different nail signs that can be associated with medical issues, though many may indicate more than one problem, according to Dr. Amy Derick, a clinical instructor of dermatology at Northwestern University.

Here are eight of the things a doctor can tell about your health based on your fingernails.

Clubbed nails. Jerry Nick, M.D. / Wikimedia Commons 1. People with emphysema and other lung problems frequently develop what's known as "clubbed" nails, according to Derick. When this happens, the fingertips become rounder and the curve of the nail changes, developing a steeper up and down pitch.

2. Small little pits or indentations can be a sign of arthritis, psoriatic arthritis, or eczema, according to Dr. Doris Day, a clinical associate professor of dermatology at New York University. Arthritis affects the joints and can be related to psoriasis, which, like eczema, affects the skin.

3. People who aren't eating well and have vitamin or dietary deficiencies may have thinner than normal nails, which are more likely to break, according to Day.

Beau's lines. Elipongo/Wikimedia Commons 4. Horizontal lines, also known as Beau's lines, are associated with serious physical stress. They look like an indented line across the nail, and frequently occur in people who have gone through chemotherapy, according to Day. They can also occur after some illnesses, injuries, or with severe malnourishment. Interestingly, there may be an altitude connection too. They've also been found in people who dove 1000 feet and others who participated in an Everest expedition.

5. Vertical lines, however, are generally not such a big deal. Some people are more genetically prone to them than others, but they're commonly associated with aging. Occasionally they may appear in malnourished people.

6. When people are iron-deficient, their nails can turn spoon-like, according to Derick. Instead of curving down and covering the finger normally, they'll start to rise up on the sides and front, going from the normal convex shape to a more concave shape, like the part of a spoon that holds liquid.

Half and half nails. Lee et al, Annals of Dermatology 7. Kidney and liver problems can create "half-and-half nails," where one part of the nail is white and the other part dark or pink, according to Derick. Kidney and liver problems frequently cause discoloration that shows up in nails and skin.

8. A nail that lifts up out of the nail bed can also indicate kidney or thyroid issues, says Derick. Many thyroid problems and autoimmune diseases like Graves or lupus create complications that dermatologists notice while examining patients.

Doctors note that because disease diagnosis is complex and some symptoms can be associated with different diseases, you should always see a medical professional if you are concerned about something you notice.