There may be loss of pigment or increased pigmentation to the skin. While many causes of pigment changes are of no medical consequence, some are good clues to other medical conditions.
Loss Of Skin Pigment - Hypopigmentation
While pigment can be lost after virtually any form of skin damage, some individuals inherit a condition called vitiligo in which pigment is spontaneously lost from various parts of the body. Others spontaneously lose pigment, seasonally or permanently only to their nose leather.
Immune-mediated disease such as pemphigus and lupus erythematosus may cause pigment loss especially in Collies and German Shepherds from one to three years old.
Increased Skin Pigmentation - Hyperpigmentation
Simple exposure to sunlight triggers pigment changes to the skin as does almost any form of chronic skin irritation or inflammation. Common causes of increased skin pigmentation include chronic allergy, Malassezia, bacterial or parasitic skin infection. Other causes include chronic hormonal imbalances
Diagnosis and treatment
A skin biopsy may be diagnostic while blood tests for underlying causes may be taken. Hyperpigmentation, often accompanied by skin thickening, resolves when the cause is removed.