Talk to Dermatologist on Brittle Nails

Hi Marham team. Need some help. My nails are very brittle and weak. There are lines and can't get smooth n shiny no matter how much i buff them or moisturize. I have consulted two dermatologists but they didn't take it seriously. ???? And on internet i have been reading that this may be an inducation of something going wrong inside. Could you plz suggest some Dr. To consult it, who can recommend any tests and fix my nails with medication or diet, whatever it needs. I really envy the ppl having shiny smooth & healthy nails. ????