How Acne Forms

1
Normal Pore

All acne is a disorder of the pilosebaceous unit, which is made of a hair follicle, sebaceous gland, and a hair. These units are found everywhere on the body except on the palms, soles, top of the feet, and the lower lip. The number of pilosebaceous units is greatest on the face, upper neck, and chest.

Sebaceous glands produce a substance called sebum, which is responsible for keeping the skin and hair moisturized. During adolescence, sebaceous glands enlarge and produce more sebum under the influence of hormones, also called androgens. After about age 20, sebum production begins to decrease.

Sebum produced by the sebaceous gland combines with cells being sloughed off within the hair follicle and "fills up" the hair follicle. When the follicle is "full," the sebum spreads over the skin surface, giving it an oily appearance. When this process works correctly, the skin is moisturized and remains healthy.

2
Early Acne - Microcomedone

Several factors contribute to the start of an acne lesion:

  • Corneocytes, or skin cells, become more "sticky" as they are shed and accumulate in the pore instead of flowing out onto the skin.
  • More skin cells are shed at the top of the pore than the bottom.
  • Sebum production is increased.

During this stage, the pore looks normal on the outside but there are distinct changes in the cells surrounding the pore. As the material in the pore builds up, it creates a bottleneck that prevents sloughing. The medical term for this stage is a microcomedone.

The bacteria Propionibacterium acnes, often shortened to P. acnes, normally resides in the pores. It uses sebum as a nutrient for growth. As sebum production increases, the number of P. acnes bacteria increases in the pore. In the microcomedone stage, the bacteria do not cause infection because they are only in the material inside the pore, not infecting the skin.

Medications that help at this stage include:

  • Over-the-counter benzoyl peroxide kills bacteria and helps prevent P. acnes from overgrowing.
  • Prescription tretinoin products like Retin-A, Retin-A Micro, and Avita reverse the "stickiness" of the skin cells, allowing them to slough normally.
  • Over-the-counter salicylic acid 2% lotion is a beta hydroxy acid that also reverses the "stickiness" of the skin cells.

3
Whitehead - Closed Comedone

As the sebum from the sebaceous gland and sloughed skin cells, also known as corneocytes, build up, they become compacted and thick. If the opening of the pore is narrow or closed, this becomes a closed comedone, also known as a whitehead.

As sebaceous material builds up, inflammation develops in the cells surrounding the pore. Whiteheads can be infected or not infected depending on whether the P. acnes bacteria have been able to infect the cells around the pore.

Medications that help at this stage include:

  • Over-the-counter benzoyl peroxide kills bacteria and helps prevent P. acnes from overgrowing.
  • Prescription tretinoin products like Retin-A, Retin-A Micro, and Avita reverse the "stickiness" of the skin cells allowing them to slough normally.
  • Over-the-counter salicylic acid 2% lotion is a beta hydroxy acid that also reverses the "stickiness" of the skin cells.
  • Prescription topical antibiotics kill the P. acnes bacteria and might be used if some of the whiteheads are infected.
  • Prescription oral antibiotics also kill the P. acnes bacteria and might be used if many whiteheads are infected or if there are infected papules or pustules.

4
Blackhead - Open Comedone

As the sebum from the sebaceous gland and sloughed skin cells, also known as corneocytes, build up, they become compacted and thick. If the opening of the pore is stays open, this becomes an open comedone, also known as a blackhead.

As sebaceous material builds up, inflammation develops in the cells surrounding the pore. Blackheads can be infected or not infected depending on whether the P. acnes bacteria have been able to infect the cells around the pore.

Medications that help at this stage include:

  • Over-the-counter benzoyl peroxide kills bacteria and helps prevent P. acnes from overgrowing.
  • Prescription tretinoin products like Retin-A, Retin-A Micro, and Avita reverse the "stickiness" of the skin cells allowing them to slough normally.
  • Over-the-counter salicylic acid 2% lotion is a beta hydroxy acid that also reverses the "stickiness" of the skin cells.
  • Prescription topical antibiotics kill the P. acnes bacteria and might be used if some of the blackheads are infected.
  • Prescription oral antibiotics also kill the P. acnes bacteria and might be used if many blackheads are infected or if there are infected papules or pustules.

5
Acne - Pimple

As the sebum from the sebaceous gland and sloughed skin cells, also known as corneocytes, build up they put pressure on the cells surrounding the pore. If enough pressure is exerted, the sides of the pore rupture and the sebaceous material leaks into the surrounding skin. Because the sebaceous material contains a lot of P. acnes bacteria, the surrounding skin now gets infected creating a red bump we know as a typical pimple. The medical term for this red bump is an inflammatory papule.

Medications that help at this stage include:

  • Over-the-counter benzoyl peroxide kills bacteria and helps prevent P. acnes from overgrowing.
  • Prescription tretinoin products like Retin-A, Retin-A Micro, and Avita reverse the "stickiness" of the skin cells allowing them to slough normally.
  • Over-the-counter salicylic acid 2% lotion is a beta hydroxy acid that also reverses the "stickiness" of the skin cells.
  • Prescription topical antibiotics kill the P. acnes bacteria and are often used if a person has some inflammatory papules.
  • Prescription oral antibiotics also kill the P. acnes bacteria and are often used if a person has a lot of inflammatory papules.

6
Acne - Pustule

A pustule is different from a pimple only because it contains white blood cells. As the immune system fights off the P. acnes infection, sometimes white blood cells (a part of the immune system) pile up creating pus in the pore. This is called a pustule. We know what parts of the immune system are involved in making pimples and pustules, but it is unclear why some lesions develop pus in them and others don't. This only matters from a scientific standpoint because, practically, pimples and pustules are treated the same way.

Medications that help at this stage include:

  • Over-the-counter benzoyl peroxide kills bacteria and helps prevent P. acnes from overgrowing.
  • Prescription tretinoin products like Retin-A, Retin-A Micro, and Avita reverse the "stickiness" of the skin cells allowing them to slough normally.
  • Over-the-counter salicylic acid 2% lotion is a beta hydroxy acid that also reverses the "stickiness" of the skin cells.
  • Prescription topical antibiotics kill the P. acnes bacteria and are often used if a person has some pustules.
  • Prescription oral antibiotics also kill the P. acnes bacteria and are often used if a person has a lot of pustules.

7
Acne - Cyst

At times when the sebaceous material and bacteria leak into the surrounding skin, the infection spreads wider and deeper causing scarring and the formation of nodules or cysts. These are the deep "pizza face" acne lesions that are very painful and resistant to over-the-counter treatments.

Medications that help at this stage include:

  • Prescription tretinoin products like Retin-A, Retin-A Micro, and Avita reverse the "stickiness" of the skin cells allowing them to slough normally.
  • Prescription oral antibiotics also kill the P. acnes bacteria and are often used to calm down the infection with cystic acne.
  • Isotretinoin (Accutane) may be prescribed to treat moderate to severe cystic acne. Accutane does have serious side effects and needs to be monitored closely if it is used.

Sources

Habif, Thomas. "Acne, Rosacea, and Related Disorders." Clinical Dermatology, 4th Edition. Ed. Thomas Habif, MD. New York: Mosby, 2004. 167-71.

Zaenglein, Andrea and Diane Thiboutot. "Acne Vulgaris." Dermatology. Ed. Jean Bolognia. New York: Mosby, 2003: 531-5.

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