Brief Answer:
It seems that you have Beau's lines.

Detailed Answer:
Hi,

You have groove like horizontal lines on nails of great toe nails. I saw the photo of your great toe nail. The lines are called Beau's lines. There may be some cause. It may be as below..

1) trauma
2) coronary occlusion
3) malnutrition
4) systemic disease
5) infection
6) chemotherapy
7) surgery
8) stress
And many others..

There may be cessation of cell division in nail matrix. Beau's line should considered as sign of systemic disease. You consult physician and have investigations to rule out systemic diseases.

I hope you got my answer. Still, any query..you are welcome.

Thanks.

Dr. Ilyas Patel MD

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