How Acne is Categorized

Non-Inflammatory Acne
Acne is typically categorized into two main types: non-inflammatory and inflammatory acne. Although there are two primary categories, there are many different types of acne which we'll discover later on. 

Non-inflammatory acne is characterized by comedones, which can be open or closed. These comedones are more commonly known as whiteheads and blackhead and are generally referred to as different types of pimples. 

Blackheads
If the pore stays open on the surface of your skin, it’s considered an open comedo, also known as a blackhead. Because the pore is open, the sebum inside the pore oxidizes upon contact with the air; this hardens the sebum, and once the air mixes with melanin skin pigment, the blackhead forms a dark coloration that can appear black, brown, or gray. Blackheads can usually be found on the nose, chin, and forehead, but might also be found on the chest, back, and arms. Blackheads tend to be rampant at the onset of puberty and during times of hormonal change.

Whiteheads
If a pore is not open and covered by a thin layer of skin, sebum and dead skin cells accumulate, resulting in a thick substance that remains stuck under the skin, forming a plug. While these are not usually infected, bacteria can affect the skin cells surrounding the pore. Whiteheads don’t usually last as long as blackheads, with an average cycle of a week. Whiteheads tend to be found on the face, but may also be observed on other parts of the body.

Inflammatory Acne
Inflammatory breakouts are a result of P. Acnes bacteria infecting the pore and causing an infection, and can often be more difficult to treat. There are four types of inflammatory acne, sometimes commonly referred to as different pimple types: papules, pustules, nodules, and cysts.

Papules 
Papules are small, raised, solid pimples that don’t contain pus and are usually the first type of inflammatory acne to affect the skin. Papules don’t display a visible pore and tend to be red in color and surrounded by swollen and inflamed tissue. They may be tender to the touch.

Pustules
Pustules are pimples that are noticeably white or yellow in the middle and are filled with pus. The marked difference between papules and pustules is that pustules contain white blood cells. When your immune system attempts to fight bacteria that’s made its way into a ruptured follicle, it will set off a buildup of white blood cells, resulting in pus production. The skin around pustules tends to be tender and inflamed.

Nodules
Acne nodules appear during the latter stages of a breakout and are usually seen in severe cases of acne. They present as large, tender bumps underneath the skin’s surface and can feel hard and stiff to the touch. Similarly to papules, nodules form from a buildup of bacteria, skin cells, and sebum in the follicles, but this formation is rooted deeper in the skin. This deep buildup can cause tissue damage to the skin and prompt the immune system to begin an inflammatory response.
While they look similar to papules, nodules are much bigger and more painful. They do not contain any pus, but can remain buried within the skin for a long time. They may be dormant and rear up in occasional bouts. If squeezed or ruptured, these nodules can spread over a larger area of the skin and cause deep infections. These lesions can cause damaging and permanent scars to the skin.

Cysts
Cystic acne is one of the hardest types of acne to successfully treat. Unlike pimples, acne cysts form deep below your skin tissue and do not come to a head. Cysts are similar to nodules, except for the presence of pus. Cysts are almost always painful to the touch and can cause great discomfort, and they don’t necessarily look like a pimple. They may just appear as a large, swollen, and red lump on the skin. They may occur independently, or you may find your skin has large clumps of cysts grouped together.

Cystic acne is less prevalent; where general acne affects 70 out of 1,000 people, cystic acne affects 2 in every 1,000 people according to Medical News Today. This severe form of Acne Vulgaris usually requires the help of a dermatologist in conjunction with self-care and preventative measures.
Inflammatory acne takes much longer to heal and can have permanent effects on the skin, so it’s important to determine the best treatment methods for your skin condition.

Sebaceous Filaments
If you’ve noticed a plethora of small grayish dots appearing across your face, especially on your nose or chin, you might incorrectly label them as blackheads. Those are actually not blackheads, they are what’s known as sebaceous filaments. These are naturally occurring hair-like formations that follow the flow of oil along the inside of a pore. If you have oily skin or larger pores, they’re more noticeable. These become visible as a pore is filled with sebum. While blackheads also begin as pores filled with sebum, it’s only once a pore is plugged with dead skin cells that it becomes an actual comedo.

It’s easy to see the difference between blackheads and sebaceous filaments when it comes to extraction. When extracted, a blackhead has a dark, hardened, plug-like appearance. Sebaceous filaments are expelled in a flowing stream of sebum that takes on a waxy consistency. You can also observe a difference in the colors of these lesions; a blackhead will be quite dark on the surface of your skin, where sebaceous filaments may be yellow-tinged, gray, or take on the hue of surrounding skin.

Even when these filaments are extracted, they generally refill with sebum within 30 days. There’s no way to completely rid the skin of these sebaceous filaments, but keeping your face clean with a regimen of regularly treating acne can help minimize their appearance and keep those pores cleaned out.

Severity Grades 
When it comes to acne diagnoses, Acne Vulgaris is measured on grades of severity, and can be diagnosed in four different classifications. 

Grade I 
Patients diagnosed with Grade I acne generally exhibit mild forms of this skin condition. Their skin may have whiteheads, blackheads, and small pimples. There’s not usually inflammation present with this type of acne breakout, and mild cases like these can often be self-diagnosed. Usually, this type of breakout occurs on the nose and forehead and most often appears in adolescence. Adults may also experience this type of acne, usually with blackheads on the nose or forehead.

Grade II
Moderate acne falls under a Grade II severity qualification. Those with this grade of acne will likely exhibit a plethora of comedones on the skin. There will be more frequent breakouts, likely accompanied by pustules and papules that may be more sensitive to the touch. 

Grade III
This grade of acne is accompanied by a large amount of inflammation in comparison to the lesser grades. The skin will exhibit numerous papules and pustules, and there may be nodules present.

Grade IV
This is the most severe form of acne, and will see skin filled with nodules, cysts, pustules, and papules. With this severity grade, acne tends to be spread across more than just the face; the back, chest, neck, and buttocks may also experience frequent breakouts. Acne of this severity can cause significant scarring and may disfigure the skin if left untreated. According to the American Academy of Dermatology, oral isotretinoin is the only medication approved to treat severe cystic acne.