Final answer:
Nail disease or deformity is generally called onychosis, which includes conditions like fungal infections and can be influenced by health problems or nutrient deficiencies.
Step-by-step explanation:
Nail disease or deformity in general is referred to as onychosis, an umbrella term for any nail deformity or disease. Onychosis can include infections, such as fungal infections (tinea unguium) often caused by dermatophytes or Candida spp., which can make the nails yellow, brittle, and prone to breaking. Furthermore, health problems like illnesses or nutrient deficiencies can significantly impact the health of nails. The nails are part of the integumentary system, and they are particularly susceptible to certain health problems due to their permeability, which can allow harmful substances to be absorbed.