Nail pitting can be caused by psoriasis, alopecia areata and atopic eczema. A few pits can be present because of trauma.
Onycholysis (distal nail plate separation) is caused by psoriasis, thyrotoxicosis, following trauma and rarely due to a photosensitive reaction to drugs such as tetracyclines.
Koilonychia (thin spoon-shaped nails) can be caused by iron deficiency anemia or rarely is congenital.
Beau's lines (transverse lines) appear as solitary depressions which grow out slowly over many months. They arise due to a severe illness or shock which causes a temporary arrest in nail growth.
Onychogryphosis is a gross thickening of the nail which is seen in later life especially in the big toe-nail. There is often a history of preceding trauma. Both psoriasis and fungal infection can also cause nail thickening.