You probably don’t spend too much time pondering about your nipples — until they command your attention. Perhaps that’s when you’re exercising without a shirt and suddenly it’s as if there are a pair of high beams protruding from your athletic bra. Or maybe every time the temperature drops below a certain level, you feel like they could slice through glass.
But what actually causes your nipples to become firm? Just as no two individuals have the precise same breast shape, nobody’s nipples react identically to different situations. However, anatomically, there is a general explanation for erect nipples.
The Science Behind Why You Experience Erect Nipples
Anatomy lesson: “Beneath the nipple and areola (the area surrounding the nipple), there are minuscule muscles that contract and tug on the skin, pushing the nipple outward,” says Michelle Lee, M.D., a cosmetic surgeon located in Beverly Hills. In response to any form of stimulation, “the sympathetic nervous system — a component of the body’s neural circuitry that accelerates your heart rate, provokes goosebumps on your skin, and induces sweaty palms — transmits signals to the nerves in those tiny muscles, causing them to contract,” she explains.
Naturally, that stimulation may be sexual. You probably already know that your nipples are a sensitive erogenous zone. Arousal — whether it’s from physical stimulation (e.g. touch) or psychological stimulation (e.g. fantasizing about something steamy and intense) — triggers specific parts of your brain that “induce those muscles in your nipples to become erect, similar to the effect that those aroused sensations can have on your genitals,” says Heather Irobunda, M.D., an obstetrician-gynecologist based in Queens, New York.
Just like a clitoris or penis, nipples consist of erectile tissue, a type of tissue that receives a substantial amount of blood flow, states Dr. Irobunda. “When the genital sensory cortex is activated, that blood flow can cause that tissue to become firmer or more rigid,” she adds. The genital sensory cortex is the same region of the brain that is stimulated by the clitoris, vagina, and cervix. Studies demonstrate that nipple stimulation — or even simply pondering about the nipples being stimulated — activates this region of the brain.
However, stimulation isn’t solely about arousal. If your nipples turn into hard as stones when the air conditioning is on high, that’s completely normal. “When the temperature drops, those minuscule muscles underneath the skin contract in order to preserve the warm air close to the skin and minimize heat loss from the radiation emitted by your skin,” explains Dr. Lee. “This is why the areola also contracts when the nipple is exposed to the cold. The contracted skin then pushes the nipple outward,” she clarifies.
And sometimes, it’s not even about stimulation. Hormones can also result in your nipples becoming erect without any other apparent cause.
Throughout your menstrual cycle or even ovulation, fluctuations in your hormone levels — particularly estrogen — may lead to an increase in sensitivity or a greater likelihood of hardness in your nipples,” states Dr. Irobunda.
Other hormone-related changes in the nipple begin during pregnancy and continue throughout breastfeeding. “During pregnancy, the hormone progesterone triggers the development of more milk lobules and duct systems,” explains Dr. Lee. Additionally, as pregnancy progresses, other hormones cause the areola to enlarge and the nipple to become erect in preparation for breastfeeding. Once breastfeeding begins, the baby’s mechanical stimulation of the nipple triggers the release of oxytocin, which causes the milk glands to contract and push milk out for the baby, according to Dr. Lee.
What About Nipple Piercings?
If you have ever noticed someone with pierced nipples, you have probably observed that their erect nipples are quite noticeable. You may wonder if these piercings affect how the nipples become hard. The answer is both yes and no.
Aside from physically pushing the nipple out by placing a large piercing at its base, “the presence of jewelry increases sensitivity due to continual nerve stimulation in the nipples,” explains Dr. Irobunda. While a nipple piercing does not mean that your nipples will be hard all the time, it can make them more noticeable. Additionally, due to increased sensitivity, they may become hard more easily.
If You’re Concerned About Your Erect Nipples (or Lack Thereof)
No matter what your nipples do, there is likely no cause for concern. “Nipples come in various shapes and sizes, and some may appear perpetually hard or never hard, depending on their size and position,” says Dr. Lee. She adds that the sensitivity of your nipples to stimulation is determined by your genetic makeup. It’s worth noting that nipples that never become hard are often referred to as flat or inverted nipples. However, if you feel self-conscious to the point where you avoid removing your shirt in a workout class or at the beach, it may be beneficial to discuss your concerns with your doctor.
On a more serious note, Dr. Lee advises that if a nipple suddenly becomes retracted or inverted, or if you observe nipple discharge, dimpling, pain, or a lump, it is important to see a doctor and determine the cause.
Furthermore, if your nipples are not only hard but also painful for an extended period of time (beyond certain phases of your menstrual cycle), Dr. Irobunda recommends seeking medical attention. This could be indicative of an underlying health issue that needs to be addressed. (See also: 11 Signs of Breast Cancer Every Woman Should Know)