My nails split vertically. they are thin, brittle, and they split to flesh. what is wrong?

Many causes: Brittle nails are not uncommon and may be due to environmental or medical conditions.Trauma, excessive wetting & drying, detergent or solvent exposure all may be casues. Underlying diseases include hypothyroidism, raynaud's disease, psoriasis, endocrine or immune disorders, pulmonary disease and some medications may also cause brittle nails. Biotin or gelatin supplementation have been suggested.