Several things cause bumps on fingernails including malnourishment, dehydration, disease, fungal infection, toxins, iron deficiency, arthritis and psoriasis according to MedlinePlus. Injury to the nail bed or nail matrix can also cause bumps and an uneven appearance. The appearance of the bumps points to the underlying cause. Pitting of the nail is most often caused by iron deficiency or psoriasis, whereas depressed lines often point to malnutrition.
According to the Skin and Cancer Center of Arizona, vertical ridges are often attributed to anemia, while horizontal ridges are most often attributed to skin inflammation caused by psoriasis or eczema, malnutrition or injury. When an injury occurs to the nail matrix found at the base of the nail, growth temporarily stops. When the nail starts growing again, there is often a thick bump running across the nail. The bump grows out and is eventually clipped off during regular grooming. Bumps and ridges become more pronounced with age due to the fact that the skin produces oil more slowly, resulting in dry skin and cuticles. Without oil to nourish them, nails become dry, brittle, cracked and bumpy. If this is the case, the nails can be nourished with topical cuticle oil to prevent further abnormalities.