A nodule is an abnormal tissue growth which can either develop just below the skin or anywhere within the skin’s three layers (the epidermis, dermis, and subcutaneous tissue). Nodules commonly form in regions such as the face, neck, armpits, and groin, although they can also develop on internal organs such as the lungs, thyroid, and lymph nodes. They create solid, raised lumps that are more than 1 to 2 centimeters in diameter, with the potential to reach up to the size of a hazelnut. Nodules are hard and firm to the touch, unlike cysts whose pus makes them softer to the touch. This type of severe acne should be consulted by a doctor, as it might be indicative of a more serious condition.
Pharaohs are recorded as having had acne, which may be the earliest known reference to the disease. Since at least the reign of Cleopatra (69–30 BC), the application of sulfur to the skin has been recognized as a useful treatment for acne.[163] The sixth-century Greek physician Aëtius of Amida is credited with coining the term "ionthos" (ίονθωξ,) or "acnae", which is believed to have been a reference to facial skin lesions that occur during "the 'acme' of life" (puberty).[164]
Azelaic acid has been shown to be effective for mild to moderate acne when applied topically at a 20% concentration.[66][129] Treatment twice daily for six months is necessary, and is as effective as topical benzoyl peroxide 5%, isotretinoin 0.05%, and erythromycin 2%.[130] Azelaic acid is thought to be an effective acne treatment due to its ability to reduce skin cell accumulation in the follicle, and its antibacterial and anti-inflammatory properties.[66] It has a slight skin-lightening effect due to its ability to inhibit melanin synthesis, and is therefore useful in treating of individuals with acne who are also affected by postinflammatory hyperpigmentation.[1] Azelaic acid may cause skin irritation but is otherwise very safe.[131] It is less effective and more expensive than retinoids.[1]

A major mechanism of acne-related skin inflammation is mediated by C. acnes's ability to bind and activate a class of immune system receptors known as toll-like receptors (TLRs), especially TLR2 and TLR4.[45][64][65] Activation of TLR2 and TLR4 by C. acnes leads to increased secretion of IL-1α, IL-8, and TNF-α.[45] Release of these inflammatory signals attracts various immune cells to the hair follicle including neutrophils, macrophages, and Th1 cells.[45] IL-1α stimulates increased skin cell activity and reproduction, which in turn fuels comedo development.[45] Furthermore, sebaceous gland cells produce more antimicrobial peptides, such as HBD1 and HBD2, in response to binding of TLR2 and TLR4.[45]
What's Going On: Do you tend to get these at the same time every month — say, just before you get your period? Because these are the work of fluctuating hormones, says Joshua Zeichner, a dermatologist and the director of cosmetic and clinical research in dermatology at Mount Sinai Hospital in New York City. Hormones can put oil production into overdrive, and having an excess of it means that it’s more likely to settle in your pores and cause zits.
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If your acne is severe, painful, or refusing to get lost, you may just be beyond what an over-the-counter treatment can do. Not only can a professional set you up with the really powerful stuff, but also Fitz Patrick explains that “working closely with an aesthetician or dermatologist means you can keep tweaking a routine to make it work best for you.”
The relationship between diet and acne is unclear, as there is no high-quality evidence that establishes any definitive link between them.[52] High-glycemic-load diets have been found to have different degrees of effect on acne severity.[7][53][54] Multiple randomized controlled trials and nonrandomized studies have found a lower-glycemic-load diet to be effective in reducing acne.[53] There is weak observational evidence suggesting that dairy milk consumption is positively associated with a higher frequency and severity of acne.[51][52][53][55][56] Milk contains whey protein and hormones such as bovine IGF-1 and precursors of dihydrotestosterone.[53] These components are hypothesized to promote the effects of insulin and IGF-1 and thereby increase the production of androgen hormones, sebum, and promote the formation of comedones.[53] Available evidence does not support a link between eating chocolate or salt and acne severity.[52][55] Chocolate does contain varying amounts of sugar, which can lead to a high glycemic load, and it can be made with or without milk. Few studies have examined the relationship between obesity and acne.[2] Vitamin B12 may trigger skin outbreaks similar to acne (acneiform eruptions), or worsen existing acne, when taken in doses exceeding the recommended daily intake.[57] Eating greasy foods does not increase acne nor make it worse.[58][59]
The treatment regimen your doctor recommends depends on your age, the type and severity of your acne, and what you are willing to commit to. For example, you may need to wash and apply medications to the affected skin twice a day for several weeks. Often topical medications and drugs you take by mouth (oral medication) are used in combination. Pregnant women will not be able to use oral prescription medications for acne.