Nails grow slowly and record what happens in your body, a bit like tree rings. Most changes are harmless, but a handful are genuinely worth a doctor visit, and one or two should not wait.
Written by Vita Globe Editorial Team | Reviewed against American Academy of Dermatology guidance, American Family Physician and peer-reviewed research
What can your nails say about your health?
Nails can reflect problems elsewhere in the body: spoon-shaped nails can point to iron deficiency, deep horizontal grooves can follow an illness or fever, and clubbing can be linked to lung or heart disease[1][2]. A new dark streak in a nail should be checked promptly because it can be a sign of melanoma[2].
Caveat: Most nail changes, like vertical ridges with age, are normal. A nail change on its own rarely diagnoses anything, which is why a clinician looks at the whole picture[1][3].
Sources: AAFP (Fawcett 2004) · AAD: 12 nail changes · Verified 2026-09-28
In this article
Why do nails reflect your overall health?
Your nails are made in the nail matrix, under the skin at the base of the nail. Anything that disrupts that area, such as a high fever, a serious illness, a nutrient shortfall or some medications, can change how the nail grows. Because nails grow slowly, the change shows up weeks later and moves toward the tip over months[3].
That is why doctors sometimes call nails a window into systemic health[3]. But most nail changes come from everyday causes like injury, picking, nail products or fungal infections.
Which nail changes mean what?
This table summarizes changes described by the American Academy of Dermatology and a review in American Family Physician[2][1]:
| Nail change | What it looks like | Possible causes |
|---|---|---|
| Vertical ridges | Fine lines running from base to tip | Usually normal aging[1] |
| Beau's lines | Deep horizontal grooves across the nail | Growth interrupted by fever, illness, injury or stress[2][1] |
| Spoon nails (koilonychia) | Thin, scooped-out nails | Iron deficiency, among other causes[2][1] |
| Pitting | Small dents in the surface | Psoriasis, dermatitis, alopecia areata[2] |
| Nail lifting (onycholysis) | Nail separates from the bed and looks white | Injury, fungal infection, psoriasis, sometimes thyroid problems[2][1] |
| Yellow nails | Thick, yellowed, slow-growing nails | Infection; rarely lung disease or rheumatoid arthritis[2] |
| Clubbing | Rounded, bulging fingertips with curved nails | Lung, heart, liver or digestive disease[2][1] |
| Washboard pattern | Ripples down the middle of the thumbnail | Habit of picking or pushing back the cuticle[2] |
Which nail changes should you get checked soon?
Most of the table above deserves a routine appointment. A few are more time-sensitive:
- A new dark streak running the length of the nail, especially on a single nail, a band that changes suddenly, or one wider than about 3mm. The AAD notes a dark streak can be melanoma[2]. Dark bands are common and often harmless in people with darker skin, but a new or changing one should still be looked at[1].
- Redness, swelling and pain around the nail, which can be an infection that is easier to treat early[2].
- Greenish-black discoloration, which can mean a bacterial infection[2].
- New clubbing, especially with breathlessness or cough[1].
Can nutrient deficiencies show up in your nails?
Yes, though less often than social media suggests. Iron deficiency is the classic example, linked to spoon-shaped nails[1]. Reviews also describe nail changes with low protein, zinc and other nutrients, mostly in people with significant deficiencies[4].
Biotin deficiency can cause brittle nails, but it is rare in people who eat a normal diet[5]. The evidence for biotin supplements improving brittle nails in people without a deficiency is limited to a few small studies without placebo groups[5]. Read more in biotin for brittle nails and signs of biotin deficiency.
One practical warning: high-dose biotin can interfere with some lab tests and cause falsely high or low results. Tell your doctor if you take it before any blood work[5]. See biotin and lab tests.
The honest summary
- Nails can reflect illness, nutrient gaps and skin conditions[3].
- Vertical ridges are usually just aging[1].
- A new dark streak needs prompt attention[2].
- Fix a deficiency if you have one; extra nutrients rarely transform healthy nails[4][5].
Our option
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Frequently asked questions
What do white spots on nails mean?
Small white spots often follow minor bumps to the nail and grow out on their own. Widespread white or pale nails can have other causes and are worth mentioning to a doctor[2].
What deficiency causes spoon-shaped nails?
Iron deficiency is the classic cause of spoon nails (koilonychia), though there are others. A blood test can check[1].
Are vertical ridges on nails a sign of illness?
Usually not. Vertical ridges are a normal part of aging[1]. See how nails change with age.
When is a dark line on a nail dangerous?
Any new, changing or widening dark streak, especially on one nail, should be checked by a dermatologist because it can be melanoma[2][1].
Can biotin fix nail problems?
Only if the cause is a biotin deficiency, which is rare. Evidence in people without a deficiency is limited[5].
Sources
- Fawcett RS, Linford S, Stulberg DL. Nail abnormalities: clues to systemic disease. Am Fam Physician. 2004;69(6):1417-1424. www.aafp.org/pubs/afp/issues/2004/0315/p1417.html
- American Academy of Dermatology Association. 12 nail changes a dermatologist should examine. www.aad.org/public/everyday-care/nail-care-secrets/basics/nail-changes-dermatologist-should-examine
- Singal A, Arora R. Nail as a window of systemic diseases. Indian Dermatol Online J. 2015;6(2):67-74. doi:10.4103/2229-5178.153002
- Cashman MW, Sloan SB. Nutrition and nail disease. Clin Dermatol. 2010;28(4):420-425. doi:10.1016/j.clindermatol.2010.03.037
- Office of Dietary Supplements, National Institutes of Health. Biotin: Fact Sheet for Health Professionals. Updated January 10, 2022. ods.od.nih.gov/factsheets/Biotin-HealthProfessional
About the Vita Globe Editorial Team
The Vita Globe Editorial Team researches and writes our wellness content, working from peer-reviewed research, systematic reviews and guidance from bodies such as the NIH and the FDA. We cite our sources inline and update articles when the evidence changes.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for medical advice. Talk to your healthcare provider before starting any new supplement, particularly if you are pregnant, nursing, taking medication, or caring for a child.
