Because of … medical reasons, says Dr Ann Robinson

Nipples are sensitive to touch, temperature and vibration – as any breastfeeding mum or nipple-pierced teen will tell you. It’s one of the parts of the body, like the clitoris or earlobes, that has lots of nerve endings that respond to sensation. That’s good when you want to be stimulated but bad when nipples start to ache with no obvious cause.

It’s natural to worry that painful nipples may be a sign of breast cancer, but it hardly ever is. Breast cancer most commonly starts as a painless lump in one breast, though occasionally a breast lump can be tender to touch. A rare condition called Paget’s disease of the nipple causes red, scaly skin (eczema) of one nipple which may itch, burn or bleed. Paget’s is often associated with an underlying cancer and, like other types of breast cancer, is more likely if you are older, female, and have a family history of breast or ovarian cancers. The bottom line is that any man or woman of any age who notices a breast lump or nipple changes should get an urgent medical opinion.

In practice, nipples usually hurt because of tiny cracks (fissures) caused by friction. Jogger’s nipple is a common hazard of long-distance running, and over-enthusiastic sucking by a baby (or sexual partner) can cause the same problem. Many women get cyclical breast pain due to hormonal fluctuations; breasts and nipples feel engorged and tender in the days leading up to a period and then improve dramatically once the period starts.

Non-cyclical breast pain is not well-understood; it doesn’t vary much with the menstrual cycle and may be part of more widespread pain conditions like fibromyalgia or inflammation in the chest wall that lies under the breasts. So nipple tenderness is rarely due to a dangerous underlying condition, but if it doesn’t get better within a few days or you have no idea what’s caused it, it’s definitely worth seeing your GP.

Because of … sex, says Nichi Hodgson

Nipple play, a long-recorded pleasure in every text from the Kama Sutra to 50 Shades of Grey, is enjoyed by both men and women alike. What makes it so enjoyable are the thousands of nerve endings our nipples contain – even male nipples each contain around 3,000 to 6,000 delicate nerve endings and around 2,000 to 4,000 erogenous nerve endings which are intertwined with the sensory touch receptors. For women, additional sensitivity comes from hormonal changes. Couple this with the fineness of the skin – just under 1mm at the thinnest point – and you begin to understand why yanking, biting or even over-robust tweaking can cause substantial pain.

Even for the most hardened masochist, nipple play should be pleasurable. It’s worth noting that the ties and weights you sometimes see in BDSM porn are there to create pleasure not when they are loaded on, but when they are released and the blood flows back into the previously restricted area, thereby increasing sensitivity and sensation. If you thought it was all about enduring weight, you can let that preconception go now, for the good of your anatomy.

The trouble is, even when you’re safely restricting with specially designed nipple ties or clamps (it’s not advisable to use wire, household pegs, or hair clips) it can be hard to know just where the comfortable threshold really lies, something which you only discover you’ve transgressed later when the play is over and the real pain rather than the sensitivity begins to set in. As a rule of thumb, if you’re still feeling the hurt four to six hours later, you’ve overdone it.

Ice wrapped in a suitable compress is best for bruising, lanolin cream for any skin breaking. And if the sensitivity is only slight, incredibly gentle “kissing better” may be an option for women – it’s been shown to cause the release of oxytocin, which acts as a natural painkiller.

Because of … running, says Adharanand Finn

If you’ve ever been out to watch a big running race such as the London marathon, particularly near the end, you will have spotted the guys with the two red circles of blood on their tops, like two gory bullet holes. It has probably made you wince, and for good reason … it hurts like hell. Yet bleeding nipples is quite preventable, and to suffer from it is a rookie mistake.

Nipples bleed from your T-shirt rubbing against them, it’s that simple. And the longer you run, the more likely it is to happen. If it’s raining, that’s also going to increase the likelihood of problems as your T-shirt becomes heavier, causing more friction. Sweating a lot on a hot day has the same effect.

To prevent bleeding, step one: avoid cotton T-shirts, as once they get wet they stay wet, unlike a “technical” running T-shirt which, in the advertising lingo, “wicks moisture away” – they do work, unless it’s a complete downpour. You’re also better off with a tighter-fitting top than with a big, oversized number bouncing around all over the place.

But even on a cool, dry day and with the right T-shirt, bleeding nipples can still be a problem if you run long enough, so, for step two, you would be well advised to go in for some localised protection. The options are many and varied. Vaseline works for a while, as do specialist lube products such as Bodyglide and Squirrel’s Nut Butter. For stronger protection – if it looks like rain, or you find you’re prone to this, or whatever other reason – a plaster over each nipple is almost fail-safe (except when it falls off); or if you want to get seriously professional, then a purpose-built protector called a Nip Guard may be called for.

Women, by virtue of tightly fitting sports bras, tend to suffer from this less, but be warned, if you run, no nipple is immune.

Because of … motherhood, says Rebecca Schiller

Are you suddenly super sensitive to your nipples and breasts being touched? Batting away your partner’s hand and wincing as you put on your bra? Tender, tingling breasts with increasingly visible veins can be one of the first signs of pregnancy. If this is you, then it’s probably time for a trip to the chemist.

Breast changes can start as early as six weeks in to pregnancy, but happily the sore nipples phase is usually confined to the first trimester, with some women describing it as an exaggerated version of the heavy tenderness they feel before their period starts. If you choose to continue with your pregnancy, you can expect your breasts to continue to grow, enlarging by at least a couple of cup sizes by the time your baby arrives. Your areola (the circle around your nipple) will grow and darken dramatically, turning it in to a target for your newborn to aim at. The little bumps on your areola (glands, called Montgomery’s tubercles) will be more obvious as they get ready to secrete a protective lubricant for your nipples.

After the birth, cool packs and very tight, supportive, non-wired bras will help get you through engorgement if you aren’t breastfeeding. If you are, then feeding your baby will relieve the pressure in your breasts that should peak approximately four days after birth when your milk comes in. Though you might feel some discomfort as you and your baby work out how to breastfeed, you shouldn’t feel much nipple pain. If your nipples are increasingly sore or become damaged, then get down to your nearest breastfeeding support group or ring the Association of Breastfeeding Mothers helpline swiftly to fine tune your technique as a duo.

Raynaud’s syndrome, thrush or changes to your older baby’s mouth due to teething can also cause temporary nipple pain. Making friends with your local breastfeeding support group early on will give you access to help from people who have seen and experienced it all. They can also advise you on minimising pain and stress whenever you and/or your child are ready to stop.