Five things you can learn about health just by looking at your fingernails.

It’s a little-known fact the state of our fingernails can be an indication of something not-quite-right internally.

While chewed nails are harmless, other visual signs can act as red flags.

Here are five things to keep an eye out for when it comes to fingernails, and exactly what each on might be signifying:

1. Vertical ridges.

So, the good news is, vertical ridges are mostly harmless.

According to Dr Jessica Krant, a fellow of the American Academy of Dermatology and assistant clinical professor of dermatology at SUNY Downstate Medical Centre, “Lengthwise ridges, if they are evenly spaced over the whole nail, are common and harmless, and generally associated with normal ageing and the nail’s increasing inability to retain moisture.”

Like wrinkles. But for your nails.

While ageing is the most common cause of ridges, they can also signify a vitamin and mineral deficiency, or in some cases, rheumatoid arthritis. If this is a concern, consult your healthcare professional.

While some people might not like the way they look, it's better not to buff off the ridges. The ridge is the thinnest spot on the nail and can split when buffed. Instead, try moisturising throughout the day with a thick lotion (Vitamin E or petroleum jelly are great), paying particular attention to the cuticle.

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2. Horizontal ridges.

Also known as Beau's lines, horizontal ridges are more likely to signify a deeper issue.

The Mayo Clinic explains, “Conditions associated with Beau’s lines include uncontrolled diabetes and peripheral vascular disease, as well as illnesses associated with a high fever, such as scarlet fever, measles, mumps and pneumonia."

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Horizontal ridges can also be a sign of zinc deficiency.

If the ridges occur on an ongoing basis, it’s a sign of a problem existing outside of the nail itself and can point to bigger problems like kidney, lung, or liver disease.

3. White marks.

These are super common. And good news: they're absolutely nothing to worry about.

Scientific name punctate leukonychia, these little white marks stem from some kind of trauma to the nail. This could be anything from slamming your nail in the boot of the car to flicking a pen - or even chewing them when you're nervous.

The white marks usually form at the base of your nail bed and over time, grow out. By the time you notice them, you've usually forgotten what caused them in the first place. Hence, the stress about what they are.

According to The Mirror, in very rare cases, if the white mark stretches across your entire nail, it could mean you've been poisoned.

But don't worry, "if you can see them...you can't have been because if you had, you'd almost certainly already be dead."

No dramas.

4. Yellow nails.

Yellow nails are most likely no big deal.

A normal sign of ageing according to Health.com, yellow nails can also result from an extensive use of nail polish or acrylic nails. Smoking may also be to blame.

If yellow nails happen to also be thicker than usual, and crumbly, it may signify a fungal infection. In that case, it's best to consult your doctor.

5. Cracking and extreme dryness.

Issues with cracking? It probably means there's not enough moisture on your nail plate.

"This could be from swimming, overuse of nail polish remover, frequent dishwashing without gloves, or just from living in a low-humidity environment," Dr. Debra Jaliman, a New York City-based dermatologist, told Health.com.

It can also happen naturally with ageing.

Note: This article is not medical advice. If you are concerned, consult your healthcare professional.