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.