A question...What are the vertical lines caused by?

Dear glowing:

From the information we found, Longitudinal Ridges (vertical lines) on the nails may possibly be due to aging, poor absorption of vitamins and minerals, thyroid disease, or an indication of a kidney problem.

If you have concerns over your nail health, the best course of action to take is to speak with your physician.

For additional information, please see our page on Fingernail Health for Stronger Harder Better-Looking Nails

Best Wishes,
-Skin Biology