How can an infected ingrown hair be treated?

An ingrown hair most often presents as small red bumps associated with local inflammation. In some cases, this skin reaction can progress to a hair follicle infection, known as folliculitis. This is generally caused by bacterial proliferation, most frequently by Staphylococcus aureus, favoured by a skin barrier weakened. Clinically, this manifests as inflammatory papules sometimes filled with pus, tender to the touch and persistent. In certain cases, the infection may develop into a cyst following an ingrown hair, or even a localized abscess requiring medical care.

The hair removal technique significantly influences the incidence of ingrown hairs.

Indeed, after shaving, hairs cut flush to the skin develop a pointed tip. During regrowth, they can curve back and re-enter the epidermis instead of passing through the skin surface, triggering a local inflammatory response. This situation creates an environment conducive to bacterial invasion and follicle infection. Other factors increase the risk of ingrown hair, notably hair type. Curly or coily hair represents a major risk factor due to the acute angle it forms with the skin surface, facilitating its penetration into the skin. Genetic predispositions have also been suggested, notably mutations of the KRT75 gene, which is involved in the structure of the hair follicle.

The pathophysiology of an infected ingrown hair relies on the hair invaginating into the epidermis, leading to local inflammation followed by infection if bacterial colonisation occurs.

Scientifically, this phenomenon is described by the term Pseudofolliculitis barbae. It is a chronic inflammatory skin condition, frequently observed following shaving, especially on the neck and cheeks, but also in areas subject to regular hair removal, such as the bikini area. In these locations, an abscess from an ingrown hair in the bikini or pubic area may occur due to hair density, local moisture and repeated friction. It is characterised by papules and pustules secondary to hair ingrowth, which in some individuals may progress to scars or keloids.

When confronted with an infected ingrown hair, the first rule is not to lance the lesion to extract the pus.

This manipulation, often performed with the fingers or a non-sterile object, favours the introduction of additional bacteria into the already infected hair follicle. It can thus aggravate the local inflammation, prolong the infection and increase the risk of complications, such as the formation of furuncles, which correspond to a deep infection of the pilosebaceous follicle.

Care is primarily based on appropriate hygiene measures. It is recommended to gently cleanse the affected area once or twice daily with lukewarm water and a mild cleanser to limit bacterial proliferation without further compromising the skin barrier. Daily application of a topical antiseptic may also be considered to reduce the bacterial load.

In certain marked inflammatory cases, the healthcare professional may also recommend a steroid cream for ingrown hairs to reduce inflammation and perifollicular oedema. It is also essential to suspend any form of hair removal or shaving on the affected area until the lesions have completely resolved, to prevent sustaining inflammation and the development of new follicular infections.

In the majority of cases, the infection associated with an ingrown hair remains superficial and transient, resolving within a few days. However, if the lesions become very painful, spread, are accompanied by systemic signs or evolve into an abscess, a dermatological consultation is required. Depending on the severity, the physician may prescribe topical or oral antibiotics to control the bacterial infection. Other local approaches may also be offered, such as benzoyl peroxide, which has antibacterial properties, or retinoids topical, which help to normalise follicular keratinisation and reduce recurrences.

In certain cases, alternative therapeutic approaches may be considered. When infected ingrown hairs result in persistent pigmented spots, particularly in darker skin phototypes, the dermatologist may recommend using depigmenting agents such as hydroquinone. This agent works by inhibiting tyrosinase, a key enzyme in the melanin synthesis process, and enables the gradual reduction of post-inflammatory hyperpigmentation.

In patients with infected ingrown hairs that are frequent and resistant to conventional measures, particularly in the context of Pseudofolliculitis barbae, laser therapy constitutes an appealing long-term option. By targeting the hair follicle and reducing hair density and stiffness, the laser reduces the risk of subcutaneous regrowth and, consequently, the associated inflammatory and infectious phenomena.

Furthermore, particularly in women, the use of topical eflornithine may also be considered. This molecule inhibits ornithine decarboxylase, an enzyme involved in hair growth, thereby slowing the rate of hair regrowth. By reducing the frequency of shaving or epilation, it indirectly helps to minimise the occurrence of ingrown hairs and related follicular infections.

Finally, when infected ingrown hairs occur in the context of excessive or unusual hair growth, an endocrinological consultation may be appropriate. A hormonal imbalance, particularly hyperandrogenism, can promote dense, coarse hair, mechanically increasing the risk of ingrown hairs and chronic folliculitis.

To minimise the risk of ingrown hair infections, stringent hygiene is indispensable, particularly during shaving or hair removal. The razor should be rinsed carefully with lukewarm water after each stroke to remove hairs, skin residues and microorganisms. It is also essential to change the blade regularly, as a blunt blade promotes micro-cuts and bacterial proliferation. Moreover, a razor is a strictly personal item: sharing it or using someone else’s significantly increases the risk of bacterial transmission, notably of Staphylococcus aureus.

Furthermore, shaving too frequently, against the grain or with excessive pressure promotes cutting of hairs beneath the skin surface, thereby increasing the risk of ingrown hairs.

To minimise the occurrence of ingrown hairs, we also recommend that you regularly moisturise and exfoliate your skin. Indeed, dry or thickened skin favours the obstruction of the hair follicle and prevents the hair from properly piercing the skin’s surface. By taking care of the skin barrier, one mechanically reduces the risk of ingrown hairs… and thus of infected ingrown hairs.

• FRIEDMAN A. J. & al. Pseudofolliculitis barbae in women: A clinical perspective. British Journal of Dermatology (2015).

• SCHWARTZ R. A. & al. Pseudofolliculitis cutis: A vexing disorder of hair growth. British Journal of Dermatology (2015).

• RASHMI S. & al. Ingrowing hair: A case report. Medicine (2016).

• WONG S. Y. & al. Preparing the hair follicle canal for hair shaft emergence. Experimental Dermatology (2021).