What causes nipple pain when you're breastfeeding or lactating and there's no visible break in the skin (though there may be redness and swelling)?

What are the two main reasons nipples become painful from breastfeeding?

When your baby sucks, a vacuum is applied to your nipple and the surrounding breast tissue and its skin.

Nipples become painful during breastfeeding for two reasons.

1. The stretching forces of your baby's sucking vacuum are concentrated on a small area of your nipple, resulting in inflammation, which causes swelling and pain. (This may also lead to a break or crack in the skin.)

2. The stretching forces of your baby's sucking vacuum cause bending of the core of your nipple, resulting in bruising and inflammation, which also causes swelling and pain.

1. The effects of concentrated stretching forces on your nipple skin

At first, skin behaves like elastic or rubber in response to stretching forces, and stretches a great deal. In the same way, your nipple skin stretches in response to the mechanical pressure generated by the vacuum inside your baby’s mouth during suckling.

This stretching is helped by the irregular ridges you might notice on the face of your nipple, which give your nipple extra stretchiness compared to other parts of your body's skin.

Finally, after quite a lot of stretching, microscopic locks turn on between the cells in the outer part of your skin (the epithelium), so that there is no more give or yielding of the skin in response to the stretching forces. After this, the skin might even break if more stretching pressure is applied. You can find out about breaks in your nipple skin here.

If the vacuum inside your baby's mouth isn't evenly distributed on the biggest possible surface area of nipple and breast tissue inside your baby's mouth, stretching forces become focussed on a small area, which can place too much strain on that part of the skin. The nipple epithelium begins to resist the stretching forces, as the locks between cells switch on.

But if too much mechanical stretching is applied to any one area of your nipple as baby’s jaw drops, the skin releases the messangers of inflammation, cytokines and histamine.

This inflammatory response switches on a cascade of signalling pathways. Pain receptors are stimulated and send messages to your brain, resulting in the perception of pain.

2. The effects of stretching forces which cause bending or deformation of your nipple core

Sometimes, the stretching pressure of the vacuum as your baby's jaw drops at the breast might result in bending or what's known as a deformation load upon the core of your nipple.

This may cause bruising, which is leakage of blood into deeper tissues. This results in inflammation without visible tissue damage.

Again, this inflammatory response switches on a cascade of signalling pathways, resulting in the experience of pain.

References

1. Pawlaczyk M, Lelonkiewicz M, Wieczorowski M. Age-dependent biomechanical properties of the skin. Postep Der Alergol. 2013;5:302-306.

2. Tepole AB, Gosain AK, Kuhl E. Stretching skin: the physiological limit and beyond. International Journal of Non Linear Mechanics. 2012;47(8):938-949.

3. Ventura AK, Lore B, Mireles O. Associations between variations in breast anatomy and early breastfeeding challenges. Journal of Human Lactation. 2020:doi:10.117/10890334420931397.

4. Vazirinejad R, Darakhshan S, Esmaeili A, Hadadian S. The effect of maternal breast variations on neonatal weight gain in the first seven days of life. International Breastfeeding Journal. 2009;4(13).

5. McClellan HL, Kent JC, Hepworth AR, Hartmann PE, Geddes DT. Persistent nipple pain in breastfeeding mothers associated with abnormal infant tongue movement. International Journal of Environmental Research and Public Health. 2015;12:10833-10845.

6. Zimmerman E, Thompson K. Clarifying nipple confusion. Journal of Perinatology. 2015;35(11):895-899.