see also:

• dermatology
• alopecia
• hyperhidrosis / excessive sweating
• hidradenitis suppurativa
• scalp folliculitis
• folliculitis
• skin_abscess

• there are three main types of dermal glands, each with their own physiologic function and skin distribution
• two of them have ducts which open into hair follicles - the sebaceous and apocrine glands whereas eccrine sweat gland ducts open directly onto skin

• hair follicles are straw-like tubes arising from a base hair bulb which is associated with a dermal papilla and its melanocytes
• hair shafts grow inside these tubes and the tubes allow the hair shaft to push upwards and out of the skin
  • if the opening of the hair follicle is damaged as in incorrect shaving, the newly growing hair shaft ends up curling under the skin layer forming a painful inflammatory ingrown hair which can become secondarily infected and form a pustule
  • if the opening of the hair follicle becomes obstructed such as by a plug of epidermal keratin or there are pathogenic bacteria within the follicle, then this can lead to folliculitis which can lead to cellulitis, boils, etc and in apocrine areas, may cause hidradenitis suppurativa
• hair shafts consist of 3 main layers - medulla, cortex and an outer cuticle
• a hair follicle is attached to arrector pili muscles which can make the hair “stand on end” (eg. as with a frightened cat)
• each hair follicle has a sebaceous gland which has a duct which opens into the upper part of the hair follicle
• pubertal hair also has apocrine sweat glands whose ducts open into the hair follicle above the sebaceous gland duct opening
• when a hair is pulled out or falls out, only the hair shaft comes out, leaving an empty hair follicle and a new hair shaft will usually form from the hair bulb at the base if the follicle is in anagen phase
  • failure of regrowth results in alopecia

• Anagen (Growth Phase):
  • cells in the root divide rapidly to build new hair.
  • it lasts 3 to 5 years for scalp hair, determining its maximum potential length.
  • 85% to 90% of hair is in this phase at any given time.
• Catagen (Transition Phase):
  • growth stops and the hair follicle shrinks.
  • the hair detaches from its underlying blood supply, forming a “club hair.”
  • this brief phase lasts only 2 to 3 weeks.
• Telogen (Resting Phase):
  • the follicle remains dormant while the detached club hair stays anchored in place.
  • this phase lasts about 3 months, during which new hair begins forming underneath.
• Exogen (Shedding Phase):
  • the old hair washes or brushes out as the new hair pushes its way up.
  • it is normal to lose 50 to 100 hairs daily during this phase

• almost all hair follicles have a sebaceous gland which has a duct which opens into the upper part of the hair follicle
• these glands secrete sebum a lipid-rich substance that coats the hair cuticle to lock in moisture, prevent brittleness, and waterproof the shaft
• the sebum also acts as an oily protection of surrounding skin to reduce it drying out
• these can block and form sebaceous cysts - often on the neck and back

• these secrete a thicker fluid containing lipids and proteins which are responsible for the “musky” odor and pheromones of adult “sweat”
• the duct of an apocrine gland empties into the upper, hollow section of the hair follicle (above the sebaceous gland duct opening) rather than opening straight onto bare skin
• these glands secrete a thicker, milky fluid containing proteins and lipids that mixes with sebum in the follicle, adding a specialized chemical coating and this lubrication mix interacts with skin bacteria to cause body odour
• the usual apocrine glands are not very active until puberty when androgens trigger secondary sex hair growth and the activation of these glands
• they are found associated with secondary sex hair and are attached to the hair follicles
  • in the axillae
  • in the groin - mainly perineum, mons pubis, scrotum, labia majoris, penis and clitoris but also any surrounding skin with pubertal hair
  • around the areolae (nipples)
  • periumbilical area
  • vermilion border of lips
• they become involved in hair follicle pathologies such as:
  • apocrine miliaria (Fox-Fordyce disease)
    • apocrine secretions become blocked
    • mainly women
    • usually presents as small itchy papules in the axillae
  • hidradenitis suppurativa (which is due to blockage of the hair follicle - usually in the axillae or groins)
    • recurrent painful boils in the axillae or groin

• a specialized form of apocrine gland which are only on eyelids (along top and bottom eyelashes)
• they secrete a substance that contributes to your eyes’ immune defenses against bacteria and other germs
• they are active from birth

• a specialized form of apocrine gland which are only in the ear canal
• they work together with sebaceous glands in the ear canal to make earwax.
• ceruminous glands contribute peptides (strings of amino acids) and antimicrobial proteins that protect ears against infection
• they are active from birth

• these are over most parts of the skin of the body and are primarily for thermoregulation to cool the body by producing mainly odorless water and salt
• their ducts open directly onto skin NOT via hair follicles - hence you can have sweaty palms
• see also hyperhidrosis / excessive sweating
• see also heat illness and heat stroke