Why is my toenail lifting? Onycholysis!

 Introduction

Onycholysis (Figure 1) is a common nail condition observed by podiatrists and other healthcare professionals, but it is seldom discussed as a single entity. This blog explores the various diagnoses that can lead to lifting of a single nail – known as "monodactylic onycholysis". As this article uncovers, monodactylic disease can be the presenting sign of nail malignancy, a condition which is often delayed in diagnosis due to their rarity. 

Figure 1 : Traumatic onycholysis affecting the hallux.

What is onycholysis?

 

Onycholysis (Figure 1), defined as the detachment or lifting of the nail plate from the underlying and/or the lateral supporting structures of the nail bed [1], is a common condition and often a cause of concern for the patient and can affect both the finger and toenails. It has a diverse range of causes from trauma and inflammatory conditions to infectious agents, tumours, chemicals but occasionally there is no known cause (idiopathic). It can often pose significant diagnostic challenges. Studies suggest it is more common in woman [2].

The condition typically begins at the onychodermal band, a distal, pink-white transverse band that serves as a protective barrier and seal protecting the nail bed from the outside environment [3]. While often initiating in the central distal part of the nail unit, it can extend to the lateral areas and proximally towards the eponychium. Clinically, onycholytic nails lose their characteristic pearly colour, becoming opaque. The ingress of water, debris and dirt can discolour the affected area (Figure 2) whilst sub-ungual hyperkeratosis may also accumulate in certain conditions.

Figure 2: Debris accumulating under an onycholytic nail. Fungal testing was negative.

The observed colours can vary; a greyish-white hue often signifies air accumulation beneath the nail plate, while yellow, brown or green discolouration may indicate secondary fungal or bacterial infection (Figure 3). Onycholysis is frequently asymptomatic and can have an acute onset or persist chronically.

Figure 3: Yellow nail discolouration from a dermatophyte nail infection

Grading of onycholysis

A simple grading system has been suggested [4]:

●      Stage I – early, initial separation of 1–2 mm of the distal nail

plate from the hyponychium (Fig. 2a).

●      Stage II – separation of the distal one-third of the nail plate.

●      Stage III – separation of one- to two-thirds of the nail plate.

●      Stage IV – onycholysis extending from the proximal nail fold

(onychomadesis) to the distal end of the nail.

●      Stage V – disappearing nail bed, i.e. when some of the nail bed/hyponychium cornifies and develops dermatoglyphics like the tip of the digit.

 Although the five-stage classification based on the degree of detachment exists, it offers limited diagnostic information regarding the underlying cause. Therefore, a detailed look into its morphology is warranted.

What causes onycholysis?

Onycholysis is broadly classified as primary (or idiopathic) when no obvious cause is identified, or secondary when linked to specific aetiologies and can affect one (“monodactylic”) or many nails.

Assessment of Onycholysis

In assessing the onycholytic nail, a good history is vital along with an appreciation of the nail affected, associated clinical conditions and signs. The use of dermatoscope can be helpful to identify signs not visible to the naked eye [5]. Typically, the nail bed can be viewed vertically and end on to visualise the free edge of the nail plate [6] assisting diagnosis. A combination of history, examination and dermoscopy can help to reach the diagnosis.

When one nail is affected (monodactylic onycholysis).

A recently published paper reviewed 7 years of cases of single digit onycholysis [7]. The profile of 49 patients identified with monodactylic onycholysis was reported. All patients underwent nail surgery for biopsy and treatment for single nail onycholysis. The average age of the cohort was 57.  The main diagnoses were as follows:

·         22% (11) Sub-ungual verrucae

·         18% (9) Psoriaform dermatitis (histology resembling psoriasis)

·         18% (9) Retronychia

·         16% (8) Mechanical Trauma

·         8% (4) Squamous cell carcinoma (1 of which was in situ)

·         8% (4) Onychopapilloma

·         4% (2) Onychomatrixoma

Interestingly in this series the toe nails were the most common followed by the thumbs (n=9). In total, 47% cases involved the hallux (n=23). Of the four cases of squamous cell carcinoma, 3 involved toenails.

Causes of monodactylic onycholysis

Onychomycosis

Dermatophyte nail infection is a very common problem, affecting around 10% of adults [8] rising significantly in older age. The most common presentation is distal lateral subungual onychomycosis (DLSO). Chronic skin infection with tinea pedis spreads into the nail bed under the nail in a distal to proximal direction [9]. Establishment of a fungal infection (or dermatophytoma [read blog here]) can lift the nail plate away from the nail bed, causing onycholysis. The extent of nail lifting is proportional to the amount of infection [10]. This often characterised by a yellow-brown discolouration (Figure 3).

Psoriasis

Psoriasis a common condition affecting around 4% of the population. Around 50%-90% of patients will at some stage develop nail lesions [11, 12] – isolated to a single nail in around 10% of patients [13]. Whilst in the fingers this tends to manifest as pitting of the nail plate, on the feet, toenails typically develop a broad onycholysis. Typical features include onycholysis, sub-ungual debris, salmon spots and rapid nail growth during active disease.  

Periungual (wart / verruca)

In most cases, onycholysis due to a periungual wart is a clinical diagnosis based on the history and naked eye examination. Dermoscopy of the lesion however can reveal finer detail to reinforce the diagnosis such as hyperkeratosis, the filiform appearance along with black dots corresponding to sub corneal haemorrhages (Read Here).

Figure 4 :Periungual wart causing the toenail to life

 Onychopapilloma

This a benign tumour arising from the distal matrix or proximal nail bed typically in middle aged adults. The longitudinal streak may appear as a red streak (erythronychia) or present as a linear onycholysis, splinter haemorrhages with splitting distally. Dermoscopy generally can confirm as, particularly with larger lesions there is a subungual localised hyperkeratotic mass evident. In one survey toenails were affected in around 5% of cases [14].

Figure 5: Onychopapilloma of the nail unit demonstrating onycholysis, splinter haemhorrages and distal, subungual hyperkeratosis (From Yun et al., (2002) under the Creative commons licence)

 Full paper: Here

Onychomatrixoma

First reported in 1992 [15], this fascinating benign fibroepithelial tumour arises from the nail matrix and presents as a tetrad of features – a yellowish, longitudinal stripe of thickened nail plate, with longitudinal over curvature frequently with splinter haemorrhages and onycholysis. The hallmark “woodworm appearance” is revealed by end on dermoscopy demonstrating the porous thickened nail plate (figure 6). Treatment is by surgical excision of the lesion, including the normal nail matrix proximal to the lesion [16].      

Figure 6: Onychomatrixoma causing distal onycholysis and the tell-tale woodworm appearance of the distal free edge under dermoscopy. (From Oak et al [2020] [16] under the creative commons licence).

 

Mechanical Trauma

Baran & Badillet highlighted the role of trauma in characterising 113 cases of onycholysis of the halluces [17]. Despite high level of onychomycosis causing distal nail lifting, in a significant proportion of patients, they identified biomechanical abnormalities such as overriding 2^nd toe, hyperextension of the 1^st IPJ and flat foot as a predictor of onycholysis in the great toenails.

Trauma of the toes in relation to foot function as a cause has also noted in other work [18]. In 2012, Zaias and colleagues coined the term Asymmetrical Gait Toenail Unit Syndrome ["AGNUS"] to explain toenail abnormalities, including onycholysis, as being due to mechanical forces of gait coupled with footwear and orthopaedic foot problems [19]. Long toenails can also predispose to onycholysis.   

Squamous Cell Carcinoma (SCCn) of the nail unit

SCCn is the most common malignancy arising in the nail unit but can be a diagnostic challenge owing to its high variability – typically diagnostic delays of around three years [20]. Monodactylic onycholysis in the early stages can be a sign as the development of a sub-ungual lesion leads to detachment of the nail plate form the nail bed. SCCn can present in three main forms – as verrucous, ulcerative or keratinous subungual lesions. SCCn of the toenail is unusual (around 2-3% of cases [20]), and thought to represent an HPV driven disease as a significant proportion of cases demonstration HPV infection. Typically, progression of the lesion leads to nail plate destruction, sub ungual oozing and frequently pain. 

Implications for practice

Onycholysis affecting one toenail has a diverse range of causes, mostly benign, but it is a symptom not a diagnosis. Firstly, on the foot onychomycosis is such a common condition it is always worth ruling this out where any fungal involvement is suspected – as the primary or secondary cause. Secondly, as noted by Robert Baran [17] and Murray [18], on the toenails, trauma plays a significant role in many cases and careful examination of the nail, foot and foot function, along with inspection of the shoes is an important part of assessment where one nail is involved – particularly the hallux. Careful questioning around family and personal history can uncover psoriasis which can affect just one nail. Additional detail from dermatoscopic examination is important to uncover other features not easily visible such as splinter haemorrhages and colour changes. In older patients, monodactylic onycholysis should always raise suspicion of a potential malignant cause, and this should always be ruled out.

References

1.         Dawber, R., et al., A Text Atlas of Nail Disorders. 2003, London: Martin Dunitz.

2.         Zaias, N., S.X. Escovar, and M.N. Zaiac, Finger and toenail onycholysis. J Eur Acad Dermatol Venereol, 2015. 29(5): p. 848–53.

3.         Perrin, C., The 2 clinical subbands of the distal nail unit and the nail isthmus. Anatomical explanation and new physiological observations in relation to the nail growth. Am J Dermatopathol, 2008. 30(3): p. 216–21.

4.         Daniel, C.R., 3rd, et al., Grading simple chronic paronychia and onycholysis. Int J Dermatol, 2006. 45(12): p. 1447–8.

5.         Ankad, B.S., et al., Dermoscopy of Onycholysis Due to Nail Psoriasis, Onychomycosis and Trauma: A Cross Sectional Study in Skin of Color. Indian Dermatol Online J, 2020. 11(5): p. 777–783.

6.         Iorizzo, M., et al., The value of dermoscopy of the nail plate free edge and hyponychium. Journal of the European Academy of Dermatology and Venereology, 2021. 35(12): p. 2361–2366.

7.         Tordjman, L., R.R. Scheinkman, and B.W. Morrison, Causes of Monodactylous Onycholysis in a Diverse Patient Population. International Journal of Dermatology, 2025. 64(10): p. 1879–1880.

8.         Gupta, A.K., D. Daigle, and M. Paquet, Therapies for Onychomycosis. Journal of the American Podiatric Medical Association, 2015. 105(4): p. 357–366.

9.         Bristow, I. and Y. Mak, Fungal foot infection - the hidden enemy. Wounds UK Journal, 2009. 5(4): p. 72–78.

10.       Gupta, A.K. and R. Pillai, The Presence of an Air Gap Between the Nail Plate and Nail Bed in Onychomycosis Patients: Treatment Implications for Topical Therapy. J Drugs Dermatol, 2015. 14(8): p. 859–63.

11.       Templeton, H.J., Onycholysis an industrial dermatosis. Journal of the American Medical Association, 1931. 97(26): p. 1950–1951.

12.       Ricardo, J.W. and S.R. Lipner, Nail Psoriasis in Older Adults: Epidemiology, Diagnosis, and Topical Therapy. Dermatologic Clinics, 2021. 39(2): p. 183–193.

13.       Chang, M.J., et al., The untold burden of isolated nail psoriasis: delayed diagnosis and significant risk of psoriatic arthritis in a retrospective study at an academic center. Journal of the American Academy of Dermatology, 2023.

14.       Starace, M., et al., Clinical and onychoscopic features of histopathologically proven onychopapillomas and literature update. Journal of Cutaneous Pathology, 2022. 49(2): p. 147–152.

15.       Baran, R. and A. Kint, Onychomatrixoma. Filamentous tufted tumour in the matrix of a funnel-shaped nail: a new entity (report of three cases). Br J Dermatol, 1992. 126(5): p. 510–5.

16.       Oak, A.S.W., et al., Honeycomb-like cavities in a single fingernail plate. JAAD Case Reports, 2020. 6(2): p. 89–91.

17.       Baran, R. and G. Badillet, Primary onycholysis of the big toenails: a review of 113 cases. Br J Dermatol, 1982. 106(5): p. 529–34.

18.       Murray, S.C. and R.P.R. Dawber, Onychomycosis of the toenails: podiatric and orthopaedic consdierations. Australasian journal of dermatology, 2002. 43(2): p. 105–112.

19.       Zaias, N., et al., The asymmetric gait toenail unit sign. Skinmed, 2012. 10(4): p. 213–7.

20.       Lipner, S.R., et al., Nail unit squamous cell carcinoma: A multicenter, retrospective study of the clinical and morphologic characteristics of 261 patients. Journal of the American Academy of Dermatology, 2026.