Left nipple pain is almost always caused by something benign, like friction, hormonal shifts, or skin irritation. The fact that it’s only on one side doesn’t automatically make it more serious. Most causes of nipple pain can affect just one nipple, and the left side isn’t inherently more worrying than the right. What matters more is the type of pain, how long it lasts, and whether you notice any visible changes.
Hormonal Shifts Are the Most Common Cause
Fluctuations in estrogen and progesterone are behind most nipple soreness. These hormones cause breast tissue and milk ducts to swell, which puts pressure on surrounding nerves. Your nipples are most likely to feel sore in the week leading up to your period, and the pain often resolves once your period starts. Though hormonal pain usually affects both sides, it’s completely normal for one nipple to be more sensitive than the other.
Other times when hormonal changes can trigger nipple pain include puberty, the early stages of menopause, and while taking hormonal birth control. If you’ve recently started or switched a contraceptive pill, patch, or IUD, that’s a likely explanation.
Pregnancy is another possibility. Breast and nipple soreness can appear as early as one to two weeks after conception, making it one of the very first symptoms. Hormones ramp up quickly to prepare the breasts for milk production, increasing blood flow and expanding the milk ducts. This soreness peaks during the first trimester.
Friction and Clothing Irritation
If you run, cycle, or do other repetitive-motion exercise, friction from your shirt or sports bra rubbing thousands of times against one nipple can leave it red, chafed, cracked, or even bleeding. One study found that nearly 36% of runners logging more than 40 miles a week experienced nipple chafing. Sweat-soaked shirts that cling to your chest make it worse, as does cold weather, which makes nipples more erect and more exposed to rubbing.
You don’t have to be an athlete for this to happen. A poorly fitting bra, a rough fabric, or even a new shirt with a stiff seam can irritate one nipple more than the other depending on how the garment sits on your body. Lightweight, moisture-wicking fabrics help. So does applying petroleum jelly or an adhesive bandage over the nipple before exercise. A snug-fitting shirt that doesn’t shift back and forth also reduces chafing.
Skin Reactions and Eczema
Your nipple skin is thinner and more sensitive than most of the skin on your body, which makes it a common spot for contact dermatitis. This is an irritation triggered by something that touches the skin: laundry detergent, body wash, lotion, or perfume. If the pain is accompanied by itching, flaking, or a rash, a product you use regularly could be the culprit.
Eczema can also develop on or around the nipple, causing dry, cracked, and sometimes weepy skin. Flare-ups tend to worsen with exposure to scented products, rough fabrics, and harsh soaps. Switching to unscented laundry detergent made for sensitive skin and avoiding lotions with artificial fragrances or dyes often makes a noticeable difference.
Infections That Cause Nipple Pain
A bacterial infection called mastitis causes the breast to feel warm, tender, and swollen, often with flu-like symptoms such as fever, chills, and fatigue. Mastitis is most common during breastfeeding, but it can happen to anyone. A yellowish discharge from the nipple is a telltale sign. Left untreated, mastitis can develop into a breast abscess, a painful pocket of pus that feels like a hard lump.
Fungal infections (thrush) look and feel different. The nipple turns pink, shiny, flaky, or blistered, with persistent soreness and sometimes deep, shooting pains in the breast. Thrush is also most common in breastfeeding, but can occur outside of it. The key difference: mastitis comes with fever and systemic illness, while thrush is more of a skin-level irritation with a distinctive shiny or cracked appearance.
Ingrown hairs around the nipple can also become infected, especially if you pluck or shave the area. This typically shows up as a localized, tender bump rather than broader breast pain.
Nipple Pain in Men
Men experience nipple pain too, and the most common cause is gynecomastia, a swelling of breast tissue driven by a hormonal imbalance between testosterone and estrogen. It typically feels like a button-sized, tender lump directly behind the nipple, and it can happen on just one side. Gynecomastia is especially common during puberty, when hormones are in flux, and it usually resolves on its own.
In adults, gynecomastia can be triggered by certain medications, including some drugs used for heartburn, hair loss, enlarged prostate, and fungal infections. Health conditions like thyroid problems and pituitary gland tumors can also cause it. If you notice a new lump under your nipple that’s tender to the touch, it’s worth getting evaluated.
When Nipple Pain Could Signal Something Serious
Breast cancer rarely presents as pain alone. In a national audit of breast cancer diagnoses, the most common presenting symptom was a lump (83%), followed by nipple abnormalities (7%) and breast pain (6%). Pain by itself, without a lump or other changes, is overwhelmingly due to a benign cause.
That said, there are specific visual changes that warrant prompt attention. Paget’s disease of the breast is a rare cancer that starts in the nipple and can mimic eczema. The warning signs include persistent flaking or crusting skin on the nipple that doesn’t heal, a nipple that flattens or inverts, and yellowish or bloody discharge. These symptoms are easy to dismiss as a skin condition, which is why Paget’s disease is often diagnosed late.
According to imaging guidelines from the American College of Radiology, nipple pain is considered potentially significant when it is focal (concentrated in a specific spot covering less than 25% of the breast), persistent, and not tied to your menstrual cycle. Cyclical pain that comes and goes with your period, or diffuse soreness spread across the breast, is not associated with cancer.
What Helps Nipple Pain at Home
For friction-related soreness, give the area time to heal by wearing soft, smooth fabrics and avoiding the activity that caused it for a few days. Petroleum jelly or a nipple balm keeps cracked skin moist while it repairs.
For suspected skin irritation, eliminate one product at a time to find the trigger. Start with laundry detergent, since it contacts your clothing all day. Switch to a fragrance-free, sensitive-skin formula and see if symptoms improve over a week or two.
For hormonal soreness, a well-fitting, supportive bra can reduce the physical impact of swollen breast tissue. Some people find that reducing caffeine intake helps with cyclical breast tenderness, though the evidence for this is mixed. Over-the-counter pain relief and a warm compress can take the edge off during the worst days of your cycle.
If the pain persists beyond a few weeks, comes with visible skin changes, or is accompanied by a lump or discharge, imaging with a mammogram or ultrasound is the standard next step to rule out anything that needs treatment.