What does it mean being flat-chested? A year old flat-chested woman Sometimes a woman's breasts don't develop much during puberty but she remains "flat-chested" — without any or much palpable breast tissue. Typically, flat-chested girls do have a nipple that looks swollen or elevated, but for some reason the breasts don't grow in size at all. Flat-chested girls do get pubic hair and start menstruating just normally AND their breasts do have milk glands — it's just that the breasts don't grow in size like most girls. Unfortunately experts like doctors and lactation consultants don't really know WHY this takes place. It has been suggested that maybe flat-chested women's breast tissue is insensitive to normal levels of circulating hormones.