INTRODUCTION — Nail ingrowing is a common nail problem that mostly affects the great toe of young adults. Fingernails are uncommonly affected. There are three different types of nail ingrowing: lateral ingrowing, distal ingrowing, and proximal ingrowing (retronychia), with distal-lateral ingrowing (onychocryptosis) being the most common. All types of nail ingrowing cause inflammation of the periungual tissues, with pain and the possible formation of granulomas.
This topic will discuss the pathogenesis, clinical presentation, and management of ingrown nails. Other nail disorders in adults and children, nail biopsy and surgery, and nail dermoscopy are reviewed separately.
EPIDEMIOLOGY — Distal-lateral ingrowing of the nail (also known as onychocryptosis) is the most common type and typically affects adolescents/young adults or older adults [1,2]. The true prevalence is unknown. In the general population, it has been estimated to be 2.5 to 5 percent. The condition is more common in males (male-to-female ratio is approximatively 2:1) in the third and fourth decades of life.
Retronychia (proximal nail ingrowing) is a relatively rare condition predominantly reported in young adult females, although it can also occur in children and older adults [3-5].
PREDISPOSING FACTORS AND PATHOGENESIS
●Distal-lateral ingrowing – In a distal-lateral ingrown nail, a sharp spicule of the distal-lateral nail plate edge penetrates and injures the soft tissues of the lateral nail fold, causing a foreign body, inflammatory, granulomatous reaction. Triggering factors include:
•Improper nail plate trimming – The spicula usually forms as a consequence of improper trimming of the distal nail plate, as patients cut the lateral edges of the nail plate to round the corners, with the purpose of preventing embedding. Self-induced trauma can also produce the spicula, which occurs in patients who tear off their nails [1,2].
•Wearing poorly fitting shoes – Pressure from shoes and weight bearing precipitate and aggravate the penetration of the spicula in the soft tissues. The embedded spicula acts as a foreign body, causing inflammation and, sometimes, secondary infection.
•Repeated, minor trauma (eg, from sports practices).
•Congenital or acquired foot deformities.
•Drug-induced paronychia – Paronychia with lateral embedding and granuloma formation can be an adverse effect of treatment with systemic retinoids, epidermal growth factor receptor (EGFR) inhibitors (eg, cetuximab, erlotinib, panitumumab, lapatinib), and antiretroviral agents. (See "Paronychia".)
●Distal ingrowing – In most cases, distal ingrowing occurs following nail plate avulsion or onychomadesis (nail shedding occurring in the setting of severe illness that may cause hypoxia of the nail matrix). Because of the loss of counterpressure due to the absence of the nail plate, the hyponychium becomes hypertrophic and prevents the nail plate from reaching the distal digit margin. This results in the embedding of the distal nail plate margin into the distal pulp .
Distal ingrowing can occur in newborns, in whom the short, soft, and thin toenails can be easily trapped into distal pulp. This may worsen by sleeping in prone position. (See "Nail disorders in children: Congenital and hereditary nail diseases", section on 'Ingrown nails'.)
●Retronychia – Retronychia is an incomplete form of nail shedding that leads to embedding of the nail into the proximal nail fold and subsequent inflammation. It is triggered by repetitive trauma or, more rarely, by a systemic condition that causes the interruption of nail growth. It has been reported after coronavirus disease 2019 (COVID-19)  or with docetaxel treatments . The nail plate does not detach from the matrix, as in onychomadesis, but remains in place instead. When the new nail plate starts growing, the old one is pushed back into the proximal nail fold, with embedding of the nail into the ventral aspect of the proximal nail fold and subsequent inflammation of the periungual skin [5,8]. Therefore, retronychia can be considered a complication of onychomadesis, where the nail plate embeds in the proximal nail fold rather than being shed.
Distal-lateral ingrowing — Distal-lateral ingrowing affects the great toe in the vast majority of cases. It can involve fingernails and multiple nails when associated with drug-induced paronychia (picture 1) (see "Paronychia", section on 'Drug-induced paronychia'). Ingrowing can occur in one or both nail edges, but the lateral edge is more commonly involved than the medial edge.
Ingrown toenail presents with a varying degree of inflammation and edema of the nail folds. The most common accompanying symptom is pain, which can be intense and debilitating. Based on the severity of inflammation and pain, three clinical stages have been described :
●Stage 1 – Stage 1 follows the initial embedding of the nail spicule into the nail fold and is characterized by slight erythema and swelling of the lateral nail folds. Patients experience pain when touching the area or wearing tight shoes.
●Stage 2 – Stage 2 is characterized by severe inflammation with redness, swelling, tenderness, oozing, and seropurulent discharge. Secondary infections can occur. Pain can be severe and alters the patient's daily activities.
●Stage 3 – Stage 3 is characterized by the formation of granulation tissue that, with time, will undergo epithelization with hypertrophy of the lateral nail fold that covers the embedded nail plate (picture 2).
Distal embedding — Distal embedding is a common complication of nail avulsion. The nail plate growth is blocked by the hyponychium, which forms a distal rim (picture 3). With time, this causes discoloration, onycholysis, and nail thickening [10,11].
Distal nail ingrowing can also occur spontaneously in infants and children, as their toenails are short, thin, soft, and brittle (picture 4). (See "Nail disorders in children: Congenital and hereditary nail diseases", section on 'Ingrown nails'.)
Retronychia — Retronychia describes ingrowth of the proximal nail plate into the proximal nail fold, with one to three nail plates misaligned beneath the uppermost nail plate (picture 5). Patients with retronychia present with acute paronychia and pain. The nail plate is often yellow in color, as the presence of subungual exudate and the other nail plates below affects its transparency, and often shows proximal onycholysis. The presence of granulation tissue between the proximal and lateral nail folds is common (picture 6) [5,8].
DIAGNOSIS — The diagnosis of lateral and distal nail ingrowing is usually straightforward, based upon history and the clinical finding of a swollen, lateral nail fold, often associated with oozing and granulation tissue formation (picture 2).
DIFFERENTIAL DIAGNOSIS — The differential diagnosis of ingrown nails includes:
●Foreign body reaction
●Congenital hypertrophy of the lateral nail fold (in the newborn) (picture 8) (see "Nail disorders in children: Congenital and hereditary nail diseases", section on 'Congenital hypertrophy of the lateral nail fold of the hallux')
●Pyogenic granuloma (picture 9) (see "Pyogenic granuloma (lobular capillary hemangioma)")
●Herpetic whitlow (picture 10)
●Subungual exostosis (picture 11)
●Fibrokeratomas (picture 12)
●Squamous cell carcinoma (picture 13)
MANAGEMENT — There are nonsurgical (conservative) and surgical approaches to the management of ingrown toenails. Evidence from several small, randomized trials suggests that surgical treatments are more effective than conservative treatments in preventing the recurrence of ingrown toenails . However, in most cases, the choice of treatment largely depends on the stage at presentation, clinician expertise, and patient preference. Some patients with mild to moderate ingrown toenail may prefer a more rapid, definitive, surgical approach than a conservative treatment.
Patient education — Patients should be educated about cutting the nail straight, without rounding the distal corners, to prevent recurrences or involvement of other nails. Wearing wide toe box or open toe shoes is recommended.
Indications and goals of treatment — A conservative approach is indicated for mild to moderate (stage 1 or 2) ingrown nails that present with slight erythema and swelling of the nail fold and moderate pain to the touch. The goals of conservative treatment include reducing inflammation and pain, protecting the nail fold from the nail plate edge, and preventing relapse or progression to a severe stage.
General measures — Patients may soak the affected foot in warm, soapy water for 10 to 20 minutes twice daily, followed by the application of a high-potency topical corticosteroid ointment for two weeks (table 1) [9,13]. High-potency topical corticosteroids have been successfully utilized in early, mild retronychia .
For distal embedding, 50% urea ointment can be applied to the distal rim and massaged in a distal-plantar direction to reduce the hypertrophic hyponychium .
Techniques — Several conservative techniques aimed at protecting the lateral nail fold from the offending nail plate edge have been described :
●Cotton nail cast (packing) – Packing is a simple technique that involves removing the nail spicule under local anesthesia and lifting and separating the offending nail edge from the adjacent soft tissue with a small piece of absorbent cotton or gauze that can be kept in place with cyanoacrylate glue . The cast should be replaced weekly, even by the patient themself, and kept in place until the lateral margin reaches the free edge. This is the author's usual conservative approach to treatment of mild to moderate ingrown toenails, as it immediately resolves the pain and is easy and fast to perform in the office.
●Dental floss – In mild cases, a variant of the packing technique utilizes a piece of dental floss placed under the nail corner to separate it from the nail fold. This procedure does not require local anesthesia .
●Taping – Taping can be used to pull the lateral nail fold away from the spicule. A piece of adhesive elastic tape is placed on the affected nail fold(s) and pulled in an oblique and proximal direction over the toe, avoiding constriction of the toe. An additional layer of tape can be used to increase stability. Patients should be instructed to replace and reposition the tape at home [2,18]. Taping requires several weeks to produce improvement. The tape adhesiveness is often limited because of hyperhidrosis or oozing granulation tissue.
●Gutter treatment – A piece of sterile plastic tube, such as a vinyl intravenous drip infusion tube, is cut lengthwise to open it. Under local anesthesia, the lateral nail margin is freed from the nail fold, and the gutter is slid over it. The gutter is fixed with cyanoacrylate glue and kept in place for six to eight weeks .
●Acrylic nail – For distal embedding, application of an acrylic nail to the distal end of the nail plate that compresses the hypertrophic hyponychium will help the distal nail to reach the tip of the digit. The acrylic nail is then removed by cutting the free edge .
Indications and goals of treatment — Surgical treatment is indicated when the condition is severe, extremely painful, or recurrent and when conservative treatments have failed. In general, stage 3 disease requires a surgical approach. (See 'Distal-lateral ingrowing' above.)
The goals of surgical treatment include a permanent reduction of the width of the nail plate by destroying the lateral horn of the nail matrix or a reduction of the periungual soft tissues, depending on the chosen surgical approach .
Surgical techniques — Various techniques have been described for the definitive treatment of ingrown nails [2,22]. In most cases, the choice depends on the clinician's surgical skills and preference. However, most authorities consider partial nail avulsion with chemical phenol matricectomy as the treatment of choice, based on its efficacy, low rate of complications, and low recurrence rate [23-25].
A 2021 Cochrane review found that the addition of chemical nail matrix ablation with phenol to partial nail avulsion resulted in a significant reduction in the risk of recurrence compared with partial nail avulsion alone . In one of the included studies, the rate of recurrence at one year was 14 percent among patients who had partial nail avulsion plus chemical matricectomy versus 41 percent among those who had partial nail avulsion alone :
●Partial nail avulsion with chemical matricectomy – This technique is the author's treatment of choice for severe distal-lateral ingrown toenail.
After local anesthesia with digital block and mechanical avulsion of the lateral portion of the nail plate (3 to 5 mm wide, on average, depending on nail size and ingrown severity), the author utilizes a cotton tip to apply phenol at 88% concentration to the lateral matrix horn for two to three minutes. As blood neutralizes phenol, it is important to apply a tourniquet to the digit to avoid bleeding. Phenol has antiseptic, anesthetic, and protein coagulant properties, which reduce postoperative pain and risk of infections. (See "Nail avulsion and chemical matricectomy", section on 'Chemical matricectomy'.)
Electrocautery and lasers are effective and safe alternatives for the destruction of the matrix horns [27,28]. However, they cause more inflammation and postoperative pain than phenol. The clinician's skills are important to ensure complete destruction of the horn, otherwise a nail spicule will grow in the proximal nail fold after surgery.
●Simple total or partial nail avulsion – Simple total or partial nail avulsion without chemical or surgical ablation of the lateral matrix is associated with high recurrence rates and is not recommended in distal-lateral embedding . (See "Nail avulsion and chemical matricectomy", section on 'Nail avulsion'.)
In contrast, simple avulsion of all superimposed nails is the treatment of choice for retronychia (see 'Retronychia' above). It allows for rapid resolution of pain and provides definitive treatment.
Postoperative care and complications — Wound care after nail avulsion and matricectomy are discussed in detail elsewhere. (See "Nail avulsion and chemical matricectomy", section on 'Wound care' and "Nail avulsion and chemical matricectomy", section on 'Complications'.)
PROGNOSIS — Recurrence of ingrown toenails is possible after all the conservative and surgical procedures discussed above. Among the surgical techniques, the risk of recurrence is lowest with partial nail avulsion and chemical matricectomy with phenol . Incomplete destruction of the lateral matrix horn results in the regrowth of a nail spicule.
SUMMARY AND RECOMMENDATIONS
●Epidemiology, predisposing factors, and pathogenesis – Nail ingrowing is a common problem that typically affects the great toenail in adolescents/young adults and older adults, with an overall estimated prevalence of 2.5 percent. Distal-lateral ingrown toenail, also known as onychocryptosis, is the most common type. It is caused by the penetration of a sharp nail spicule into the lateral nail fold, resulting in a foreign body, inflammatory reaction. Predisposing factors include improper nail trimming; wearing poorly fitting shoes; hyperhidrosis; repeated, minor trauma (eg, from sports practices); or congenital or acquired foot deformities. (See 'Predisposing factors and pathogenesis' above.)
●Clinical presentation – Ingrown toenail presents with a varying degree of inflammation and edema of the nail fold, ranging from mild erythema and edema (stage 1), to severe inflammation with seropurulent discharge (stage 2), to formation of granulation tissue and chronic hypertrophy of the nail fold (stage 3) (picture 2). Pain may be intense and debilitating. (See 'Clinical presentations' above.)
●Diagnosis – The diagnosis of ingrown toenail is clinical, based upon history and clinical findings.
●Management – There are nonsurgical (conservative) and surgical treatment options for ingrown toenails. The choice of treatment largely depends on the stage at presentation, clinician's expertise, and patient preference:
•Conservative treatment – Mild to moderate ingrown toenails (stage 1 and 2) can be treated conservatively with several techniques, including cotton nail cast (packing), taping, gutter treatment, and nail bracing (picture 14). The cotton nail cast is the author's preferred approach, as it immediately resolves the pain and is easy and fast to perform in the office. (See 'Conservative treatment' above.)
•Surgical treatment – Surgical treatment is indicated for severe ingrown toenails (stage 3) and ingrown toenails that have failed conservative treatments. Partial nail avulsion with chemical matricectomy using 88% phenol is the author's preferred approach, based on its low risk of complications and low recurrence rate. (See 'Surgical treatment' above.)
●Prognosis – Recurrence is possible with all conservative and surgical techniques. Incomplete destruction of the lateral matrix horn results in the regrowth of a nail spicule. (See 'Prognosis' above.)