treatment response. salicylic acid salicylic acid is a topically applied beta-hydroxy acid that stops bacteria from reproducing and has keratolytic properties. it is less effective than retinoid therapy. salicylic acid opens obstructed skin pores and promotes the shedding of epithelial skin cells. dry skin is the most commonly seen side effect with topical application, though darkening of the skin can occur in individuals with darker skin types. other medications topical and oral preparations of nicotinamide (the amide form of vitamin b3) are alternative medical treatments. nicotinamide reportedly improves acne due to its anti-inflammatory properties, its ability to suppress sebum production, and its wound healing properties. topical and oral preparations of zinc are suggested treatments for acne; evidence to support their use for this purpose is limited. zinc's capacities to reduce inflammation and sebum production as well as inhibit c. acnes growth are its proposed mechanisms for improving acne. antihistamines may improve symptoms among those already taking isotretinoin due to their anti-inflammatory properties and their ability to suppress sebum production. hydroquinone lightens the skin when applied topically by inhibiting tyrosinase, the enzyme responsible for converting the amino acid tyrosine to the skin pigment melanin, and is used to treat acne-associated post-inflammatory hyperpigmentation. by interfering with the production of melanin in the epidermis, hydroquinone leads to less hyperpigmentation as darkened skin cells are naturally shed over time. improvement in skin hyperpigmentation is typically seen within six months when used twice daily. hydroquinone is ineffective for hyperpigmentation affecting deeper layers of skin such as the dermis. the use of a sunscreen with spf 15 or higher in the morning with reapplication every two hours is recommended when using hydroquinone. its application only to affected areas lowers the risk of lightening the color of normal skin but can lead to a temporary ring of lightened skin around the hyperpigmented area. hydroquinone is generally well-tolerated; side effects are typically mild (e.g., skin irritation) and occur with the use of a higher than the recommended 4% concentration. most preparations contain the preservative sodium metabisulfite, which has been linked to rare cases of allergic reactions, including anaphylaxis and severe asthma exacerbations in susceptible people. in extremely rare cases, the frequent and improper application of high-dose hydroquinone has been associated with a systemic condition known as exogenous ochronosis (skin discoloration and connective tissue damage from the accumulation of homogentisic acid). combination therapy combination therapy—using medications of different classes together, each with a different mechanism of action—has been demonstrated to be a more effective approach to acne treatment than monotherapy. the use of topical benzoyl peroxide and antibiotics together is more effective than antibiotics alone. similarly, using a topical retinoid with an antibiotic clears acne lesions faster than the use of antibiotics alone. frequently used combinations include the following: antibiotic and benzoyl peroxide, antibiotic and topical retinoid, or topical retinoid and benzoyl peroxide. dermatologists generally prefer combining benzoyl peroxide with a retinoid over the combination of a topical antibiotic with a retinoid. both regimens are effective, but benzoyl peroxide does not lead to antibiotic resistance. pregnancy although sebaceous gland activity in the skin increases during the late stages of pregnancy, pregnancy has not been reliably associated with worsened acne severity. in general, topically applied medications are considered the first-line approach to acne treatment during pregnancy, as they have little systemic absorption and are therefore unlikely to harm a developing fetus. highly recommended therapies include topically applied benzoyl peroxide (pregnancy category c) and azelaic acid (category b). salicylic acid carries a category c safety rating due to higher systemic absorption (9–25%), and an association between the use of anti-inflammatory medications in the third trimester and adverse effects to the developing fetus including too little amniotic fluid in the uterus and early closure of the babies' ductus arteriosus blood vessel. prolonged use of salicylic acid over significant areas of the skin or under occlusive (sealed) dressings is not recommended as these methods increase systemic absorption and the potential for fetal harm. tretinoin (category c) and adapalene (category c) are very poorly absorbed, but certain studies have suggested teratogenic effects in the first trimester. the data examining the association between maternal topical retinoid exposure in the first trimester of pregnancy and adverse pregnancy outcomes is limited. a systematic review of observational studies concluded that such exposure does not appear to increase the risk of major birth defects, miscarriages, stillbirths, premature births, or low birth weight. similarly, in studies examining the effects of topical retinoids during pregnancy, fetal harm has not been seen in the second and third trimesters. nevertheless, since rare harms from topical retinoids are not ruled out, they are not recommended for use during pregnancy due to persistent safety concerns. retinoids contraindicated for use during pregnancy include the topical retinoid tazarotene, and oral retinoids isotretinoin and acitretin (all category x). spironolactone is relatively contraindicated for use during pregnancy due to its antiandrogen effects. finasteride is not recommended as it is highly teratogenic. topical antibiotics deemed safe during pregnancy include clindamycin, erythromycin, and metronidazole (all category b), due to negligible systemic absorption. nadifloxacin and dapsone (category c) are other topical antibiotics that may be used to treat acne in pregnant women but have received less study. no adverse fetal events have been reported from the topical use of dapsone. if retinoids are used there is a high risk of abnormalities occurring in the developing fetus; women of childbearing age are therefore required to use effective birth control if retinoids are used to treat acne. oral antibiotics deemed safe for pregnancy (all category b) include azithromycin, cephalosporins, and penicillins. tetracyclines (category d) are contraindicated during pregnancy as they are known to deposit in developing fetal teeth, resulting in yellow discoloration and thinned tooth enamel. their use during pregnancy has been associated with the development of acute fatty liver of pregnancy and is further avoided for this reason. procedures limited evidence supports comedo extraction, but it is an option for comedones that do not improve with standard treatment. another procedure for immediate relief is the injection of a corticosteroid into an inflamed acne comedo. electrocautery and electrofulguration are effective alternative treatments for comedones. light therapy is a treatment method that involves delivering certain specific wavelengths of light to an area of skin affected by acne. both regular and laser light have been used. the evidence for light therapy as a treatment for acne is weak and inconclusive. various light therapies appear to provide a short-term benefit, but data for long-term outcomes, and outcomes in those with severe acne, are sparse; it may have a role for individuals whose acne has been resistant to topical medications. a 2016 meta-analysis was unable to conclude whether light therapies were more beneficial than placebo or no treatment, nor the duration of benefit. when regular light is used immediately following the application of a sensitizing substance to the skin such as aminolevulinic acid or methyl aminolevulinate, the treatment is referred to as photodynamic therapy (pdt). pdt has the most supporting evidence of all light therapy modalities. pdt treats acne by using various forms of light (e.g., blue light or red light) that preferentially target the pilosebaceous unit. once the light activates the sensitizing substance, this generates free radicals and reactive oxygen species in the skin, which purposefully damage the sebaceous glands and kill c. acnes bacteria. many different types of nonablative lasers (i.e., lasers that do not vaporize the top layer of the skin but rather induce a physiologic response in the skin from the light) have been used to treat acne, including those that use infrared wavelengths of light. ablative lasers (such as co2 and fractional types) have also been used to treat active acne and its scars. when ablative lasers are used, the treatment is often referred to as laser resurfacing because, as mentioned previously, the entire upper layers of the skin are vaporized. ablative lasers are associated with higher rates of adverse effects compared with non-ablative lasers, with examples being post-inflammatory hyperpigmentation, persistent facial redness, and persistent pain. physiologically, certain wavelengths of light, used with or without accompanying topical chemicals, are thought to kill bacteria and decrease the size and activity of the glands that produce sebum. disadvantages of light therapy can include its cost, the need for multiple visits, the time required to complete the procedure(s), and pain associated with some of the treatment modalities. typical side effects include skin peeling, temporary reddening of the skin, swelling, and post-inflammatory hyperpigmentation. dermabrasion is an effective therapeutic procedure for reducing the appearance of superficial atrophic scars of the boxcar and rolling varieties. ice-pick scars do not respond well to treatment with dermabrasion due to their depth. the procedure is painful and has many potential side effects such as skin sensitivity to sunlight, redness, and decreased pigmentation of the skin. dermabrasion has fallen out of favor with the introduction of laser resurfacing. unlike dermabrasion, there is no evidence that microdermabrasion is an effective treatment for acne. dermal or subcutaneous fillers are substances injected into the skin to improve the appearance of acne scars. fillers are used to increase natural collagen production in the skin and to increase skin volume and decrease the depth of acne scars. examples of fillers used for this purpose include hyaluronic acid; poly(methyl methacrylate) microspheres with collagen; human and bovine collagen derivatives, and fat harvested from the person's own body (autologous fat transfer). microneedling is a procedure in which an instrument with multiple rows of tiny needles is rolled over the skin to elicit a wound healing response and stimulate collagen production to reduce the appearance of atrophic acne scars in people with darker skin color. notable adverse effects of microneedling include post-inflammatory hyperpigmentation and tram track scarring (described as discrete slightly raised scars in a linear distribution similar to a tram track). the latter is thought to be primarily attributable to improper technique by the practitioner, including the use of excessive pressure or inappropriately large needles. subcision is useful for the treatment of superficial atrophic acne scars and involves the use of a small needle to loosen the fibrotic adhesions that result in the depressed appearance of the scar. chemical peels can be used to reduce the appearance of acne scars. mild peels include those using glycolic acid, lactic acid, salicylic acid, jessner's solution, or a lower concentration (20%) of trichloroacetic acid. these peels only affect the epidermal layer of the skin and can be useful in the treatment of superficial acne scars as well as skin pigmentation changes from inflammatory acne. higher concentrations of trichloroacetic acid (30–40%) are considered to be medium-strength peels and affect the skin as deep as the papillary dermis. formulations of trichloroacetic acid concentrated to 50% or more are considered to be deep chemical peels. medium-strength and deep-strength chemical peels are more effective for deeper atrophic scars but are more likely to cause side effects such as skin pigmentation changes, infection, and small white superficial cysts known as milia. alternative medicine researchers are investigating complementary therapies as treatment for people with acne. low-quality evidence suggests topical application of tea tree oil or bee venom may reduce the total number of skin lesions in those with acne. tea tree oil appears to be approximately as effective as benzoyl peroxide or salicylic acid but is associated with allergic contact dermatitis. proposed mechanisms for tea tree oil's anti-acne effects include antibacterial action against c. acnes and anti-inflammatory properties. numerous other plant-derived therapies have demonstrated positive effects against acne (e.g., basil oil; oligosaccharides from seaweed; however, few well-done studies have examined their use for this purpose. there is a lack of high-quality evidence for the use of acupuncture, herbal medicine, or cupping therapy for acne. self-care many over-the-counter treatments in many forms are available, which are often known as cosmeceuticals. certain types of makeup may be useful to mask acne. in those with oily skin, a water-based product is often preferred. prognosis acne usually improves around the age of 20 but may persist into adulthood. permanent physical scarring may occur. rare complications from acne or its treatment include the formation of pyogenic granulomas, osteoma cutis, and acne with facial edema. early and aggressive treatment of acne is advocated by some in the medical community to reduce the chances of these poor outcomes. mental health impact there is good evidence