The earliest pathologic change is the formation of a plug (a microcomedone), which is driven primarily by excessive growth, reproduction, and accumulation of skin cells in the hair follicle.[1] In normal skin, the skin cells that have died come up to the surface and exit the pore of the hair follicle.[10] However, increased production of oily sebum in those with acne causes the dead skin cells to stick together.[10] The accumulation of dead skin cell debris and oily sebum blocks the pore of the hair follicle, thus forming the microcomedone.[10] This is further exacerbated by the biofilm created by C. acnes within the hair follicle.[45] If the microcomedone is superficial within the hair follicle, the skin pigment melanin is exposed to air, resulting in its oxidation and dark appearance (known as a blackhead or open comedo).[1][10][20] In contrast, if the microcomedone occurs deep within the hair follicle, this causes the formation of a whitehead (known as a closed comedo).[1][10]
^ White, Stephen D.; Bordeau, Patrick B.; Blumstein, Philippe; Ibisch, Catherine; GuaguÈre, Eric; Denerolle, Philippe; Carlotti, Didier N.; Scott, Katherine V. (1 September 1997). "Feline acne and results of treatment with mupirocin in an open clinical trial: 25 cases (1994–96)". Veterinary Dermatology. 8 (3): 157–164. doi:10.1046/j.1365-3164.1997.d01-16.x. ISSN 1365-3164.

Finally, we included light therapy devices that treat acne. These are not the laser devices that the dermatologist uses. Instead, these are tools you can use at home to clear up your skin. They usually work best on your face where there is less tissue for the light to penetrate. Plus, you can treat yourself with light therapy at the same time you use salicylic acid or benzoyl peroxide, too.

Hormonal treatments for acne such as combined birth control pills and antiandrogens may be considered a first-line therapy for acne under a number of circumstances, including when contraception is desired, when known or suspected hyperandrogenism is present, when acne occurs in adulthood, when acne flares premenstrually, and when symptoms of significant sebum production (seborrhea) are co-present.[128] Hormone therapy is effective for acne even in women with normal androgen levels.[128]
Atrophic acne scars have lost collagen from the healing response and are the most common type of acne scar (account for approximately 75% of all acne scars).[32][33] They may be further classified as ice-pick scars, boxcar scars, and rolling scars.[31] Ice-pick scars are narrow (less than 2 mm across), deep scars that extend into the dermis.[32] Boxcar scars are round or ovoid indented scars with sharp borders and vary in size from 1.5–4 mm across.[32] Rolling scars are wider than icepick and boxcar scars (4–5 mm across) and have a wave-like pattern of depth in the skin.[32]
In the simplest sense, acne is caused when pores containing hair follicles and sebaceous (oil) glands become clogged. The sebaceous gland is responsible for producing sebum, an oily substance necessary for skin to stay hydrated and soft. However, too much sebum can plug the opening at the top of the pore, trapping a buildup of oil, dead skin cells, and bacteria leading to acne lesions.
Rosemary oil has been around for years and used topically for acne and inflamed skin. (15) A Chinese study concluded that rosemary essential oil helps decrease acne due to its antibacterial effects. To better understand the effects, the study increased the concentration of the rosemary essential oil, resulting in severely damaged bacterial bodies. Treated bacteria eventually led to bacterial death. (16) 

Rosemary oil has been around for years and used topically for acne and inflamed skin. (15) A Chinese study concluded that rosemary essential oil helps decrease acne due to its antibacterial effects. To better understand the effects, the study increased the concentration of the rosemary essential oil, resulting in severely damaged bacterial bodies. Treated bacteria eventually led to bacterial death. (16) 
What to know about hormonal imbalances While it is natural to experience hormonal imbalances at certain times in life, such as puberty, menopause, and pregnancy, some hormonal changes are related to underlying medical conditions. This article looks at the causes and symptoms of hormonal imbalances in men and women, as well as treatment and home remedies. Read now
How to Handle It: If you've tried the usual anti-acne ingredients, like salicylic acid and benzoyl peroxide (which, we should warn you, rarely work for this), you should consider paying your dermatologist a visit. "You may need a cortisone injection or an oral medication, like an antibiotic, in addition to topical formulas," says Zeichner. He's also a fan of a prescription topical medication called Epiduo Forte Gel, since, he says, it's been shown to be effective at controlling severe acne without the help of oral treatments.
Scars (permanent): People who get acne cysts and nodules often see scars when the acne clears. You can prevent these scars. Be sure to see a dermatologist for treatment if you get acne early — between 8 and 12 years old. If someone in your family had acne cysts and nodules, you also should see a dermatologist if you get acne. Treating acne before cysts and nodules appear can prevent scars.
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