Most of the time, dark pink lines on a women’s breast are stretch marks – which look like spoke-like lines. They appear on the skin during periods of rapid physical growth (such as puberty, pregnancy, or with weight gain). During puberty, stretch marks on the breasts are very common and completely normal. Other common places for stretch marks are on the hips and thighs. Over time, the stretch marks will fade to match your normal skin color (usually within 1 to 2 years). However, if any area of your breast is red, warm to the touch, and you have a fever, it’s likely that you have an infection and you should see your health care provider as soon as possible.