Pain in just one nipple is common and usually caused by something minor like friction, a skin irritation, or hormonal changes. In most cases it resolves on its own or with simple adjustments. That said, one-sided nipple pain has a wider range of possible causes than you might expect, and understanding what’s behind it helps you figure out whether it needs attention.
Friction and Skin Irritation
The most common reason for one nipple to hurt is mechanical irritation. Clothing that rubs unevenly, a bra that fits differently on one side, or a workout shirt made from synthetic fabric can create soreness on just one nipple while leaving the other fine. Runners are especially familiar with this: repetitive friction over miles can cause raw, painful skin on one or both nipples, but it often hits one side harder depending on how your shirt sits.
Laundry detergents, soaps, lotions, and perfumes can also trigger irritation or eczema on the nipple. Sweat trapped under a bra makes it worse. If you’re noticing redness, dryness, or flaking alongside the pain, the culprit is likely contact irritation. Switching to cotton bras and shirts, using unscented detergent, and applying petroleum jelly or a ceramide-based moisturizer to restore your skin barrier usually clears it up within a few days.
Hormonal Breast Pain
Hormonal changes during the menstrual cycle are one of the most common causes of breast and nipple pain in people who menstruate. Cyclic breast pain typically starts in the second half of your cycle, when rising levels of estrogen and progesterone stimulate breast tissue, and eases once your period begins. This type of pain is usually bilateral, felt in both breasts, and tends to concentrate in the upper outer area. But it doesn’t always show up symmetrically. One breast may have denser tissue or respond more strongly to hormonal shifts, making the pain feel one-sided.
Non-cyclic breast pain is different. It tends to be constant or intermittent, more common after age 40, and more often affects just one side, sometimes in a single area. Causes include cysts, changes in the milk ducts, stretched ligaments in the breast, hormone replacement therapy, and lifestyle factors. If your nipple pain doesn’t follow your cycle and stays on one side, non-cyclic causes are worth considering.
Breastfeeding-Related Causes
If you’re breastfeeding, one-sided nipple pain is extremely common and usually stems from a latch issue. When a baby doesn’t latch deeply enough, the nipple gets compressed and damaged, sometimes on just the side where positioning is trickier. Over time this can lead to cracked, bleeding nipples.
Milk blebs (also called nipple blisters) are another frequent cause. These are small white, yellow, or clear dots that form on the nipple when a milk duct opening gets blocked. They can be surprisingly painful, especially during feeding. The standard approach is rest, ice, and over-the-counter pain relievers. Picking at them or poking them with a needle can cause infection and should be avoided.
Mastitis, an infection of the breast tissue, often starts on one side. Symptoms include warmth, swelling, a wedge-shaped area of redness, burning pain during feeding, and sometimes fever above 101°F. It requires prompt treatment with antibiotics because untreated mastitis can progress to an abscess.
Nipple Pain in Men
Men can develop one-sided nipple pain too, and it’s more common than many people realize. The most frequent cause is gynecomastia, a swelling of breast tissue driven by an imbalance between estrogen and testosterone. It can affect one or both sides, sometimes unevenly, causing tenderness, swelling, and sensitivity when the nipple rubs against clothing. Teenagers going through puberty are especially prone to it, and it usually resolves on its own.
Several medications can trigger gynecomastia, including certain HIV treatments, ADHD medications containing amphetamines, anti-anxiety drugs like diazepam, tricyclic antidepressants, some antibiotics, and opioids. If your nipple pain started after beginning a new medication, that connection is worth raising with your prescriber.
When Pain Signals Something More Serious
Most people searching this question are wondering whether nipple pain could mean cancer. The reassuring answer is that pain alone is rarely a sign of breast cancer. A large study in primary care found that among women who visited their doctor specifically for breast pain, only about 1 to 3% were ultimately diagnosed with cancer. Painless lumps are actually more predictive of cancer than painful ones.
That said, there is a rare condition called Paget’s disease of the breast that starts at the nipple and is linked to an underlying cancer. It looks like eczema but doesn’t respond to eczema treatment. Signs include flaky or scaly skin on the nipple, crusty or oozing patches, straw-colored or bloody discharge, and thickening of the skin. It almost always affects just one side. If your nipple has visible skin changes that aren’t improving, that warrants a medical evaluation.
Other red flags that should prompt a visit to your doctor include nipple discharge (especially if bloody or spontaneous), a new lump, nipple retraction where the nipple pulls inward, or persistent pain lasting more than a couple of weeks without an obvious cause.
Simple Steps That Help
For garden-variety nipple soreness on one side, a few practical changes often resolve it. Switch to soft cotton bras and tops, and make sure your bra fits properly on both sides. Apply petroleum jelly or a ceramide cream to protect the skin. Avoid scented products near your chest. If you run or exercise frequently, consider nipple covers or bandages to reduce friction.
If the pain follows your menstrual cycle, tracking it over two or three months helps confirm the pattern. Cyclic pain that arrives predictably and resolves with your period is almost always benign, even if it feels alarming in the moment. A well-fitting, supportive bra during the second half of your cycle can reduce discomfort noticeably.
For pain that’s persistent, worsening, or accompanied by skin changes or discharge, imaging such as ultrasound or mammography can help identify structural causes like cysts, duct changes, or, rarely, something more concerning. Your doctor will choose the type of imaging based on your age, symptoms, and breast density.