Brief Answer:
Nothing serious at all, here is what can cause this

Detailed Answer:
Hello sir and welcome.

Thank you for writing to us.

I have gone through your query with diligence and would like you to know that I am here to help. I would be more than happy to help you with the most likely causes in your case sir:

+Nutrient deficiency (e.g. zinc, iron, vitamin D, vitamin B12, etc)
+Age-related
+Thyroid abnormality
+Eczema
+If you have been plucking your eyebrows, then this could also result in hair loss over time

In my opinion there is nothing to worry about at all, it could be any of the above causes, most of which are fine. But during your next doctors visit, just make sure you are elaborately evaluated so we can correct anything you are lacking (e.g. nutrient-wise, thyroid correction, etc.)

I hope you find my response helpful. Please feel free to write back to me for any further clarifications, I am always here to help.

Best wishes.

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