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Line on left hand thumb
Hello Doctor,
I have this line on my left thumb. It is there as it is since around 8 months now. It has not grown darker or wider.
Would vitamin deficiency also cause this?
I am really worried. No history otherwise.
Please suggest. Attached are two photos. First from February and latter current one.
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A single persistent line on the thumbnail (likely a vertical brown/black line) is usually called longitudinal melanonychia → Longitudinal Melanonychia
Next Steps
• No urgent treatment needed
Health Tips
• Avoid repeated trauma (nail biting, pressure)
• Maintain nail hygiene
• You can still check:
– Vitamin B12, iron (general health)
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Usually these lines on the nails appear with iron and calcium deficiencies. If left unattended, the nails can become brittle too. Get your blood tests done for iron studies, haemogram, calcium, alkaline phosphotase, VIT D and review for further management
Next Steps
Get the tests done
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A stable vertical line on the nail for months is harmless and not due to vitamin deficiency.
It can be due to minor trauma or pigmentation smoking can contribute.
No need to worry unless it increases in size, becomes darker, or spreads to surrounding skin.
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The thin vertical line on your thumb nail, which has been stable for 8 months without changing in width or color, is most likely a condition called Melanonychia. While vitamin deficiencies (especially B12) can sometimes cause nail discolorations, they usually present more diffusely. Since there is no history of sudden change or 'Hutchinson's sign' (extension of pigment to the nail fold), it is likely benign. However, any pigmented line on a single nail warrants a baseline clinical examination to rule out more serious causes."
Next Steps
Keep monitoring the line every few months. If you notice it becoming wider (especially more than 3mm), darker, or if the edges become blurred, you should consult a dermatologist immediately. For now, try to recall any minor trauma to the thumb base 8-10 months ago, as even small injuries can leave a lasting mark on the nail plate."
Health Tips
"Do not try to scrape or file the nail to remove the line, as the pigment originates from the nail matrix (under the skin) and not the surface. Avoid self-medicating with high-dose vitamins without a confirmed deficiency, as it won't resolve the line if the cause is non-nutritional. A simple dermoscopic examination by a specialist can provide 100% peace of mind."
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Don’t worry, it usually resolves on its own.
There are many possible reasons for this, but in your case are you on long-term antibiotics? If yes, that might be one of the causes.
Otherwise, it could be due to a vitamin deficiency (especially B12) or possibly related to trauma.
Next Steps
Try multivitamins for a month
And if it progresses more, than consult a Dermatologist
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Hi dear,
It is melanonychia. It is usually a benign condition usually followed by minor nail bed trauma due to melanin deposition. In your case it looks harmless as it does not reach nailfold/cuticle.
Next Steps
Be re-assured and just be watchful for any future changes in colouration/ darkening or widening of this line or if it reaches nail fold where nail originates.
Health Tips
Visit a dermatologist if in case it shows above mentioned changes. Rest be re-assured.
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