Acne will usually have a straightforward cause. See: acne what is it (what causes acne). Some types, however, do not fit into the usual categories. Most of these are rare but include the following:

Acne conglobata

This type of acne usually affects more men than women and is most likely to occur between the ages of 18 and 30 years. It may occur on the site of an existing papule, pustule or comedone or on an area of skin previously affected by acne.

This rare and serious type of inflammatory acne requires aggressive treatment. Even with treatment, it may leave the skin scarred and permanently damaged. It is characterised by large cysts that are interconnected beneath the skin, forming ‘tracts’ or visible lumps that join one another. Even after clearing the pus-filled cysts and spots, it is possible that they will again become inflamed, resulting in the problem returning. This will usually occur in one concentrated area of the body, such as the buttocks. It is a painful and disfiguring condition, requiring immediate help from a dermatologist. Usually the strongest acne treatments will be prescribed and, if necessary, a course of steroids will also be prescribed.

Acne fulminans

This rare type of acne will be aggressive, painful and inflamed in a similar way to acne conglobate. It can start very quickly and in some cases become severe in a matter of weeks. Where it differs is that it may present with painful joints along with aches and pains similar to those experienced in arthritis. It may also be accompanied with a fever. This rare condition is documented in boys, rarely in females, and may be linked to the adrenal glands that release hormones. Its exact cause is not known. Acne fulminans can be treated with steroids, but will not usually respond to antibiotics in the way that other types of acne will.

Hidradenitis suppurativa

This condition is linked to acne but affects only certain sweat producing lands (apocrine glands). Unlike normal sweat glands which are triggered by overheating, the apocrine glands are triggered by stress, hormonal changes such as menstruation or sexual stimulation. Hidradenitis suppurativa occurs in the armpits, nipples and the genitoanal region (the buttocks and genitals). Apocrine glands are stimulated by another hormone called adrenaline. This condition may be connected to acne because it is often present only in people who have acne vulgaris.

The key signs of this condition are deep-seated nodules or lumps around the breasts, armpits or the genitoanal region. These may appear in isolation or in a group and the condition tends to continually relapse.

The lesions are made up of deep cysts and nodules with tract formation similar to acne conglobata. Scarring is again common and secondary infection frequently occurs. This affects more women than men and is common in people who are overweight. If this type of acne fails to respond to aggressive treatments, it may be likely that the blockages will require surgery to help drain them. They will be packed with sterile dressings and allowed to heal. This condition is very distressing and painful. There is a dedicated support group called the British Association for Hidradenitis Suppurativa. Their website is http://www.hstrust.org.

Hidradenitis suppurative - technical article

Dissecting cellulitis of the scalp 

This is similar to acne conglobata (see above) with the presence of cysts, nodules and interconnected tracts. However when it is located on the scalp, it often leads to scarring; this in turn leads to hair loss in those areas, and secondary infection may be common. This may respond quite well to steroid injections directly into the lesions, which can be painful and should be carried out by a specialist.

Acne mechanica

This might also be called ‘friction acne’ as it is often the result of anything that traps heat against the body for a prolonged period of time, or rubs or puts pressure on the skin. Any keen sportsman or woman who is also prone to acne may find that sports equipment pushed or held tightly next to skin, such as baseball caps, helmets and sweatbands, brings on a breakout in these areas.

Until quite recently, anyone with moderate to severe acne was disqualified from joining the armed forces. It was feared that tropical humid weather conditions in war zones or practice areas might worsen existing acne where heavy armour or packs were worn in close contact with the skin. This ruling has changed, but anyone carrying heavy weights or equipment which is in prolonged contact with a sweating body should be aware that it can aggravate existing acne. In tropical areas, this can lead to potentially serious consequences such as the blood infection septicaemia, which can be life-threatening if not treated quickly.

It is not uncommon for acne to develop under tight bra straps, on the inner thighs or around areas of tight clothing that attract sweat. Even excessive phone use could, in theory, cause a similar problem. Maybe this condition could be called ‘mobile phone acne’. This type of acne can be helped by reducing the pressure of tight clothing and carrying wet wipes to regularly remove excess sweat in the affected areas. Removing the sweat helps to reduce the problem.

Acne Majorca

This type of acne was first described in the 1970’s when northern Europeans found that cheap holiday destinations such as Spain offered plenty of sun at affordable prices. Some people believe that sunlight can help their acne; indeed the UV light may well kill off bacteria and sterilise existing acne. However UV exposure also promotes a thickened, horny layer of skin. This layer can more easily obstruct the follicle of the sebaceous glands. The improvement in the skin is usually short term and lasts little longer than the tan itself. The result of obstructing the skin, however, is to make acne worse. In addition to this, oily sun creams and lotions can themselves cause an outbreak of acne. Always use acne-friendly brands that are oil free.

Drug-induced acne

As the title suggests, some types of acne will flare up as a result of drugs taken either for medical conditions or (illegally) for muscle-building effect. One mood stabiliser, lithium, will often trigger acne in patients. For those who need the benefits of a drug such as lithium, any resulting acne should be easy to control by taking anti-acne medication at the same time.

Steroids are used for hormone-related conditions but are also taken illegally by body-builders who will commonly source them to help ‘bulk-up’ their muscles quickly. They will often buy them from the internet or dealers. These might have the effect of building muscles quickly, but the side-effect of acne is common. Frighteningly, many will again turn to illegal sources to obtain powerful acne treatments that may also have serious side-effects. People who get caught in this dangerous loop are risking their health and wellbeing for the sake of a sport and their appearance.

Gram-negative folliculitis

This rare condition can easily be mistaken for acne vulgaris (common acne) because it occurs as a result of using long-term antibiotic medication prescribed to treat the acne vulgaris. If individuals with acne experience a sudden flare up after their skin has been clear for a while, and if they are taking a long-term course of antibiotics, the possibility of gram-negative folliculitis should be considered and investigated.

There are two types of gram-negative folliculitis. In 80% of people, there will be superficial pustules without comedones that extend from the nose area to the chin and cheeks. In 20% of cases, deep nodular and cystic spots will be seen (large, hard-feeling spots or softer red lumps, both of which are over 5 mm in diameter).

Treating this successfully can be very challenging, although some improvement is seen with isotretinoin (Roaccutane). Clues as to whether you might have gram-negative folliculitis include:

• You have used systemic antibiotics (antibiotics taken by mouth) for prolonged periods.
• You have a flare up of pustular or cystic type spots that are resistant to the usual treatments.

Gram-negative organisms tend to be harboured in the nose, so testing for this condition will usually require a painless swab from inside the nostril. Sebum on the skin (the oiliness responsible for acne) provides an ideal moist environment for the bacteria to thrive. Antibiotics often fail to solve the problem, possibly because they may kill the bacteria, but have no effect on the sebum.