3.13: Sweat and Sebaceous Glands
- Page ID
- 128817
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Your skin contains two main types of glands: sweat glands, which help cool the body, and sebaceous (oil) glands, which keep the skin and hair moisturized.
- Compare and contrast eccrine and apocrine sweat glands.
- Explain the function of sweat.
- Describe the location and function of sebaceous glands.
Sweat Glands: Your Skin's Built-In Cooling System
Sweat glands, also known as sudoriferous glands, are simple tubular structures found almost everywhere on the body. Their primary function is to regulate temperature.
Each sweat gland is made up of two parts:
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A secretory portion, where sweat is produced.
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An excretory duct, which carries the sweat to the body surface to be excreted.
Sweat is produced in the coiled secretory portion of the sweat gland. This portion is typically located in the dermis, but in some cases, it may extend into the hypodermis. From there, the excretory duct carries the sweat upward through the dermis and into the epidermis, where it opens at a pore on the surface.
Humans have two main types of sweat glands: eccrine and apocrine glands. Eccrine glands are distributed across most of the body and are primarily responsible for regulating body temperature by producing a watery, odorless sweat. In contrast, apocrine glands are concentrated in specific areas such as the armpits and groin. They produce a thicker, milky fluid that, when broken down by skin bacteria, can lead to body odor. Together, these sweat glands play essential roles in thermoregulation and the body's response to stress.
Eccrine Glands
The most numerous types of sweat glands in our skin, found almost everywhere on the body, are called eccrine sweat glands. These are the true sweat glands in the sense of helping to regulate body temperature. Sweating cools the body through the process of evaporative cooling.
When your internal temperature rises, sweat glands release a clear, odorless substance (sweat) consisting primarily of water and NaCl onto the surface of your skin. The key to cooling is not just the presence of sweat, but its evaporation. As sweat evaporates, it absorbs heat from your skin because the process of turning water (sweat) into vapor requires energy — specifically, the "heat of vaporization." This energy comes from your body's heat, which is carried away with the vapor, lowering your skin and body temperature. This mechanism is especially important when environmental temperatures are high, since evaporation can still remove heat even if the air temperature is close to or above body temperature.
Apocrine Glands
Apocrine sweat glands are large, specialized glands mainly found in areas with hair follicles such as the armpits (axillae), groin, around the nipples (areola), and the perianal region. Unlike eccrine glands, which open directly onto the skin, apocrine glands release their secretions into hair follicles just below the skin surface. While apocrine glands exist at birth, their significant activity starts during puberty, likely due to hormonal influences.
Apocrine glands produce a thick, oily, and initially odorless secretion containing water, lipids, proteins, and steroids. Their excretions are converted by skin bacteria into various chemicals we associated with body odor. Apocrine sweat glands play virtually no role in body temperature regulation; their primary function in humans is thought to be related to scent release rather than cooling.
Structurally, these glands share some basic features with the eccrine glands — they both consist of a secretory coil (where sweat is produced) and a duct (which transports sweat). However, they differ in several key aspects: apocrine glands are larger and their secretory portion is bigger, with a larger lumen. Additionally their ducts open into hair follicles rather than the skin surface.
Modified apocrine glands include mammary glands (which produce milk), ceruminous glands (which produce earwax), and ciliary glands (on the eyelids).
While the exact function of apocrine glands is still not fully understood, we do know they become active during times of stress, pain, and sexual arousal — though the reasons behind this are not yet clear. Similarly, the purpose of body oder in humans is not completely known, but research suggests it may play an important role in communication. Body odor may act as a chemical signal, helping to share information about a person’s identity, emotional state, or even genetic compatibility when choosing a mate.
Figure \(\PageIndex{1}\): Human Skin. Cross sectional image of skin showing the two types of sweat glands and a sebaceous gland.
Sebaceous Glands
Sebaceous glands (also known as oil glands) are the sebum producing glands of the dermis. Sebum is an oily substance, composed mostly of lipids mixed with epithelial cell debris. It plays a key role in lubricating and waterproofing the skin and hair, helping to keep them soft, supple, and protected against drying and external damage.
Sebaceous glands develop from the epithelial cells of the hair follicle itself (specifically the external root sheath of the hair follicle). Their ducts thus usually open up into the upper part of a hair follicle, called the infundibulum. However, some sebaceous gland ducts open directly onto our skin surface such as at the corner of the mouth and the glans penis.
They function through a holocrine secretion process, meaning the entire gland cell fills with sebum and then ruptures to release its oily content. The cells are continuously regenerated from the gland’s periphery.
Sebaceous glands are active from birth, producing a waxy coating that protects newborn skin. They become particularly active during puberty under hormonal influence. Their secretions also have antimicrobial properties, contributing to skin defense.
While the sebaceous glands are present just about all over the skin, they are notably absent on the palms of the hands and the soles of the feet. The sebum being excreted by your body today began production around 8 days ago.
As mentioned earlier, sebum acts as a natural lubricant that helps moisturize the skin. It does this by slowing down the evaporation of water from the skin’s surface. Sebum also plays a protective role by limiting the growth of certain bacteria. It contains antimicrobial compounds that help prevent bacteria from penetrating deeper layers of the skin. In addition, sebum helps condition the hair, keeping it from becoming too dry or brittle.
Sebaceous glands are involved in several common skin conditions. During puberty, hormonal changes trigger these glands to produce more sebum, which often leads to oily skin. If a sebaceous duct becomes clogged with sebum, it can form a whitehead. If that trapped material dries and oxidizes, it darkens into a blackhead. When a sebaceous gland becomes infected, it can lead to more serious forms of acne. (See the last page of the study guide for more details on acne.)