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Science & Nature • Anatomy

Nipple

A nipple is a small raised structure at the center of the breast.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

A nipple is a small raised structure at the center of the breast. In humans and other mammals, it is the external opening through which milk can pass during lactation, and it is usually surrounded by the areola. The nipple is composed of smooth muscle, connective tissue, milk ducts, and nerves.

Structure

The nipple is a modified patch of skin at the centre of the breast. It contains smooth muscle, connective tissue, milk ducts, and many sensory nerves. The nipple is usually more pigmented than the surrounding skin. Typical size is about 10–12 mm wide and 9–10 mm protrusion.

Function

The nipple's primary function is to deliver milk from the breast during breastfeeding. Milk exits through small openings connected to lactiferous ducts. The nipple also has a sensory role due to its rich nerve supply, and it can contribute to sexual pleasure.

Variation

Nipple appearance varies widely between individuals. Common forms include protruding, flat, and inverted nipples. Size and position can change with age, sex, and lactation.

The areola is the darker skin surrounding the nipple. Together, the nipple and areola are referred to as the nipple-areolar complex. The areola may contain sebaceous glands such as Montgomery glands.

Key facts

  • The nipple is the small central structure on the breast, surrounded by the areola; together they form the nipple-areolar complex.
  • Milk exits through small openings in the nipple during lactation.
  • The nipple contains smooth muscle, connective tissue, ducts, and many nerves.
  • Nipple shape varies and may be protruding, flat, or inverted.
  • The nipple has a sensory role and can contribute to sexual pleasure.
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Canadian context

Canadian readers may encounter nipple anatomy in breastfeeding education, breast health screening, and clinical discussions of breast and nipple conditions.

Frequently asked questions

What is a nipple?
A nipple is a small raised structure at the centre of the breast that serves as an opening for milk flow during lactation.
What is the areola?
The areola is the darker area of skin surrounding the nipple, and together they are called the nipple-areolar complex.
Do all nipples look the same?
No. Nipples can be protruding, flat, or inverted, and their size and shape vary from person to person.
How many openings does a nipple have?
A nipple has multiple small openings for milk ducts; sources vary, commonly describing about nine or about 15–20 duct openings.
What is the main function of the nipple?
Its main function is to deliver milk from the breast during breastfeeding.
Does the nipple have nerves?
Yes. The nipple is richly supplied with nerves, which makes it sensitive to touch and stimulation.

References

  1. Cleveland Clinic — https://my.clevelandclinic.org/health/body/nipple
    Supports: Definition, anatomy, areola relationship, variation, function, and approximate size
  2. Elsevier — https://www.elsevier.com/resources/anatomy/integument/skin/nipple/17022
    Supports: Anatomical structure, size, nipple-areolar complex, ducts, muscle, and location
  3. NCBI Bookshelf (StatPearls) — https://www.ncbi.nlm.nih.gov/books/NBK519575/
    Supports: Breast/nipple anatomy and location, breastfeeding relevance
  4. PubMed Central / NIH — https://pmc.ncbi.nlm.nih.gov/articles/PMC4716863/
    Supports: Nipple and areola as the nipple-areolar complex
  5. National Cancer Institute — https://www.cancer.gov/publications/dictionaries/cancer-terms/def/nipple
    Supports: Concise anatomical definition and milk flow
  6. PubMed — https://pubmed.ncbi.nlm.nih.gov/26242366/
    Supports: Review of nipple anatomy, physiology, and benign pathology