Nipple sensitivity is very common. Whether your nipples feel sensitive because of arousal, an ill-fitting bra, or the weather outside (especially cold weather), your nipples can react. If they do, there’s no need to worry. Considering where they are on your body, it would be a bit confusing if they weren’t sensitive from time to time.

“There are distinctions between nipple pain/discomfort, nipple sensitivity, nipple erection, and nipple stimulation,” says holistic wellness speaker Dr. Donna L. Hamilton. “Depending on the factors like the amount of discomfort and personal pain threshold, some women might describe nipple pain as nipple sensitivity and vice-versa.” In other words, what one woman might describe as merely sensitive, another might describe as painful. And, of course, if you’re dealing with constant pain, it may be time to see a doctor.

So, what are the most common reasons for nipple sensitivity?

1. A poorly fitting bra. If you’re wearing a bra that doesn’t fit the way it should, it can definitely create some sensitivity. Your nipples can become sore, itchy, dry, and if you’re a runner who doesn’t have a sports bra that fits, as it should, you can also experience bleeding. When it comes to purchasing a bra, it’s always best to go with fabric that breathes, like cotton. If you’re someone who prefers to wear lace bras, then at least get a lace bra with a cotton lining. You want to keep the friction levels against your nipple to a minimum.

2. Sexual arousal. “An interesting study found that when nipples are stimulated, they ‘light up’ on fMRI — the same area of the brain that stimulates genitals also ‘lights up,’” explained Dr. Hamilton. “In other words, the same area of the brain is responsible for registering/processing stimulation of the nipples, the vagina, clitoris, and uterus.”

But although, as Dr. Hamilton added, nipple stimulation travels to the same part of the brain as that of the vagina, clitoris, and uterus, nipple stimulation doesn’t always equate with sexual arousal for every woman. Of course there are those women who swear they can climax strictly by nipple stimulation, but they’re definitely few and far between.

3. Breast-feeding. Of course the very thought of a baby sucking on your nipple, even one who has yet to grow any teeth, can make some women shudder. According to Dr. Hamilton, this is a common reason for sensitivity in nipples. An especially uncomfortable sensitivity of the nipples can be exacerbated if the baby “isn’t latching on correctly.” It can take time for the nipple to somewhat toughen up to its new role as food provider. So, in the meantime… ouch.

4. Allergic reactions. Because nipples are so sensitive, they can easily be affected by outside sources. While we already know that the temperature can cause nipples to either remain flat or become erect, in a similar response as goosebumps when we’re cold, another reason for create sensitivity is the products we use.

While new lotions and shower gels may be a cause, another more common product that can induce sensitivity is laundry detergent. If you’re finding that no matter what clothes you put on your body, your nipples just are not having it, it’s time to immediately find another laundry detergent with fewer irritants in it, ideally something a bit more natural in its ingredients.

5. Hormonal shifts in the body. Both a woman’s breasts and her nipples tend to be more sensitive at different times during her cycle because of the changes in levels of estrogen and progesterone. It is completely normal for both the breast and nipple, and even the areola, to feel most sensitive during menstruation.

“It’s also important to make a distinction between breast sensitivity and nipple sensitivity,” explained Dr. Hamilton, “Breast tenderness usually refers to sensations in the full part of the breast and nipple tenderness specifically to the nipple (and possibly the areola.)”

So while they are two entities, they do work together in many ways. Because of this, it’s definitely something to keep an eye on if things start feeling too sensitive to bear. It may just mean that you need to quit wearing your wool sweater without a bra (friction!), or something more serious. You should always be aware of your body and any differences, in it or on it, that might arise.