Skin darkening or hyperpigmentation in dogs is usually due to an excessive amount of melanin in the cells. Melanin is a substance or pigment that gives the dog skin and hair color.
Melanin occurs in all mammals in two forms: eumelanin and pheomelanin. Eumelanin is a black or dark brown pigment. Pheomelanin gives a yellowish tinge. Melanin synthesizes specialized cells, melanocytes, which are found in the skin, the root of the hair and other places in the body, at the stimulation of the metabotropic hormone.
The melanocytes are concentrated in the form of small pigment particles (melanosomes) which are then transported by the cell shoots of the melanocytes into the surrounding keratinocytes. Localized darker pigmentation occurs in skin areas where melanocytes are particularly concentrated and active.
This is either due to an increased number of melanocytes or increased production of melanin and its deposition in the basal epithelium. This happens either secondary to inflammation or nevertheless idiopathic (primary).
One reason for this change is atopic dermatitis. The most commonly affected areas of the dog are the groin, armpits and the places between the toes. As a reaction to an undesirable irritation, the skin itself changes color over time. Instead of pale pink color, it develops a darker, even blacker color, especially in those areas where the skin has become inflamed.
In addition to hyperpigmentation, macules or blemishes may occur on the skin, primarily characterized by discoloration of the skin. The macules are localized changes, limited and less than 1 cm in size, while the spots are less restricted and much larger in size.
For your safety as well as your pet’s health, it would be a good idea to have your pet examined by a veterinarian for starters. She will be able to perform a complete examination of the skin and hair, and then further, in accordance with the diagnosis, will advise you and answer any questions.