The mammary gland is composed of a combination of three different types of tissue: glandular tissue (which secretes human milk), connective or fibrous tissue, as well as adipose tissue. The relative proportion of each of these tissues varies greatly for the same person, according to the time of life, but also from one person to another.
The predominance of adipose tissue, which changes with age, favours the interpretation of images created after a mammogram, because the fat is not very dense and results in a black image. Therefore, tumour lesions (spots, artifacts or whitish calcifications) that one attempts to detect by this examination will be much more visible on a black greasy background, than on a white background of glandular or fibrous tissue.
Hormone therapy generally stimulates tissue density.
The dominant composition of breast tissue often determines the clinical appearance of the breast. Thus, a fatty breast will be much more flexible and carry fewer nodules than a glandular breast, which will be firmer and often more painful, especially before menstruation.