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Published on: 8/20/2026
Black streaks in nails, medically known as melanonychia, are dark vertical lines that appear on the fingernails or toenails. While often harmless, they can have several causes, including:
Because melanonychia has both harmless and serious causes, identifying the underlying reason matters. If you've noticed a new or changing dark streak, don't guess — get clarity in minutes. Take a free, instant, online symptom check to better understand your symptoms and confidently plan your next steps.
Reviewed for medical accuracy: 07/15/2026
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Black streaks in nails, called melanonychia, can happen for different reasons. Sometimes, these streaks are present from birth, which is known as congenital longitudinal melanonychia. This is generally not a cause for concern and is considered a normal variation.
Melanonychia can also occur during pregnancy. This is often due to hormonal changes and is usually temporary. Pregnant individuals might notice these streaks appearing or becoming more pronounced.
However, it's important to be aware that while many cases of melanonychia are harmless, there can be situations where it might need further examination. If the streaks change in appearance, such as becoming wider or darker, or if they are accompanied by other symptoms, you can use our free AI symptom checker to better understand what might be causing your nail changes and whether you should seek medical attention.
In summary, while black streaks in nails are not always a cause for concern, monitoring any changes and consulting a healthcare provider if needed is a good practice.
(References)
Skornšek N, Orešič Barač T, & Marko PB. (2017). Congenital longitudinal melanonychia: a case report. Acta dermatovenerologica Alpina, Pannonica, et Adriatica, 29264905.
Kouskoukis CE, Scher RK, & Hatcher VA. (1982). Melanonychia striata longitudinalis. A case report. The Journal of dermatologic surgery and oncology, 7076969.
Plachouri KM, Kolonitsiou F, & Georgiou S. (2019). Melanonychia Striata: Nail Alterations during Pregnancy. Skinmed, 31904335.
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