Nail disease covers a surprisingly wide range of conditions, from common fungal infections and ingrown toenails to rare cancers and signs of organ failure visible through the nail plate. The nail itself is a small, dense structure made of hardened keratin, produced by a specialized tissue called the matrix that sits just beneath the base of the nail. Because the nail grows slowly and records insults over time, it can act as a kind of biological diary, reflecting infections, medications, autoimmune conditions, and even anxiety disorders. Understanding the major categories of nail disease helps you know when a cosmetic nuisance needs patience and when a subtle color change deserves a dermatologist’s attention.
Fungal Nail Infections
Onychomycosis, the medical term for fungal infection of the nail, is by far the most common nail disease worldwide. It accounts for up to about 30% of all diagnosed superficial fungal infections.1PubMed. Mycology of nail disorders Three broad groups of fungi cause it: dermatophytes (which feed on keratin and are the dominant culprits), yeasts such as Candida, and nondermatophyte molds.2PubMed Central. Onychomycosis: pathogenesis, diagnosis, and management Toenails are affected far more often than fingernails, partly because shoes create the warm, moist environment fungi love and partly because toenails grow more slowly, giving the infection more time to establish itself.
A typical case starts at the free edge or side of the nail. The nail turns yellow or brown, becomes thickened and crumbly, and may separate from the nail bed underneath. It is rarely painful in the early stages, which is one reason people often ignore it for months or years. But leaving it untreated does not just affect appearance. The infection can spread to other nails and to the surrounding skin, and in people with diabetes or suppressed immune systems, a crumbling nail can become a gateway for bacterial infections.
Treatment depends on severity. Topical antifungal lacquers work for mild cases limited to the tip of the nail, but most moderate-to-severe infections need oral medication. A large Cochrane review found high-quality evidence that oral terbinafine is far more effective than placebo for achieving both clinical cure and elimination of the fungus.3Cochrane Database of Systematic Reviews. Oral antifungal medication for toenail onychomycosis Even with effective drugs, you should expect the nail to look abnormal for months after the fungus is gone, because healthy nail has to grow out from the base to replace the damaged plate. For toenails, that process can take a year or more.
Green Nail Syndrome and Other Bacterial Infections
Not every discolored nail is fungal. If your nail has turned green, green-black, or green-yellow, the likely cause is Pseudomonas aeruginosa, a bacterium that thrives in wet environments. Green nail syndrome, also called chloronychia, typically shows up in people whose hands spend a lot of time in water, soap, or detergents, and it is especially common among elderly individuals.4PubMed Central. Chloronychia: green nail syndrome caused by Pseudomonas aeruginosa in elderly persons The infection settles in where the nail has already loosened from the bed, a condition called onycholysis, and the distinctive green color comes from pigments the bacteria produce.
Treatment usually involves keeping the affected area dry and applying topical antiseptics, though oral antibiotics such as ciprofloxacin may be necessary, particularly in older patients.5PubMed Central. Chloronychia: green nail syndrome caused by Pseudomonas aeruginosa in elderly persons The key practical takeaway is that green or black discoloration of a nail warrants a medical evaluation rather than an assumption that it is a bruise or a fungal infection.
Nail Psoriasis and Its Link to Arthritis
Psoriasis does not just affect the skin. Nearly half of people with skin psoriasis develop nail changes, and the proportion climbs to roughly 80% in those who also have psoriatic arthritis.6PubMed Central. Nail involvement in psoriatic arthritis The nails can show pitting (small dents in the surface), thickening, crumbling, oil-drop discoloration (yellowish-brown spots under the nail), and onycholysis. These changes are more than cosmetic frustrations. The presence of nail disease in someone with psoriasis is a strong predictor that psoriatic arthritis may develop or already be present.
A cross-sectional study found nail involvement in about two-thirds of psoriatic arthritis patients, with transverse grooves showing the strongest association with the disease.7Journal of the American Academy of Dermatology. Nail findings in patients with psoriatic arthritis: A cross-sectional study with special reference to transverse grooves Severe nail disease also correlated with worse skin psoriasis, more aggressive joint disease, and higher scores for depression and anxiety.8Rheumatology. Extended report: nail disease in psoriatic arthritis—clinically important, potentially treatable and often overlooked If you have psoriasis and notice new nail changes, it is worth flagging them to your doctor even if they seem minor, because they can influence decisions about systemic treatment.
Ingrown Toenails
Ingrown toenails, known clinically as onychocryptosis, are one of the most painful and common nail problems. The nail edge digs into the surrounding skin fold, triggering inflammation, swelling, and sometimes infection. Tight shoes, improper trimming (rounding the edges rather than cutting straight across), and genetic nail curvature all play a role.
Mild cases can improve with warm soaks, properly fitted footwear, and careful trimming. But recurrent or severe ingrown nails often need a procedure to remove the offending nail margin and destroy the strip of matrix that produces it. The two main approaches are chemical matricectomy, where phenol or sodium hydroxide is applied to the matrix, and surgical excision. A randomized trial comparing phenol matricectomy with an aesthetic surgical reconstruction technique found recurrence rates below 3% for both methods, though healing took about three weeks with the chemical approach versus roughly one week with surgery.9PubMed Central. The Treatment of Ingrown Nail: Chemical Matricectomy With Phenol Versus Aesthetic Reconstruction. A Single Blinded Randomized Clinical Trial A larger retrospective study confirmed that no single technique clearly outperforms the others in terms of recurrence, suggesting that surgeon experience and patient-specific factors matter more than the particular method chosen.10PubMed Central. Long-Term Outcomes of Surgical and Chemical Matricectomy for Ingrown Toenail Management: A Retrospective Study
Nails as a Window to Internal Disease
Some of the most diagnostically useful nail changes are not diseases of the nail itself but reflections of something happening elsewhere in the body. Two classic examples are Terry’s nails and Lindsay’s nails. Terry’s nails appear mostly white with a narrow pink or brown band at the tip, and they are associated with liver cirrhosis, heart failure, and type 2 diabetes. Lindsay’s nails, sometimes called half-and-half nails, split into a white zone covering the proximal portion and a red or brown zone covering the distal portion; they are linked to chronic kidney disease.11PubMed Central. Terry’s Nails and Lindsay’s Nails: Two Nail Abnormalities in Chronic Systemic Diseases Neither condition is painful or harmful on its own, but recognizing the pattern can prompt a workup that catches serious organ disease earlier.
Digital clubbing is another important systemic sign. The fingertips become bulbous, and the angle between the nail and the cuticle area flattens or reverses so the nail curves downward like a watch glass. The exact cause is still debated, but growth factors such as platelet-derived growth factor and vascular endothelial growth factor have been implicated.12PubMed Central. Digital clubbing Clubbing can appear with lung cancer, chronic lung infections, inflammatory bowel disease, liver disease, and certain heart conditions. When it develops quickly, especially in a smoker, it warrants prompt investigation.
Nail Melanoma and Dark Streaks
A dark band running lengthwise on a nail is a common and usually harmless finding, particularly in people with darker skin tones, where melanocyte activation in the nail matrix frequently produces longitudinal pigmented bands. However, the same appearance can occasionally be the first sign of subungual melanoma, a rare but serious cancer. Features that raise suspicion include asymmetric, irregular bands with multiple colors, a width of at least 3 mm, and pigment that spreads beyond the nail onto the surrounding skin, a finding known as the Hutchinson sign.13JAMA Dermatology. Assessment of a Predictive Scoring Model for Dermoscopy of Subungual Melanoma In Situ A predictive scoring model using these dermoscopic features achieved a sensitivity of 89% for distinguishing early melanoma from benign pigmentation.14JAMA Dermatology. Assessment of a Predictive Scoring Model for Dermoscopy of Subungual Melanoma In Situ
Broadening of the band over time, especially if it becomes irregular or multicolored, is a red flag that should prompt a dermatology referral.15PubMed. Diagnosis and treatment of nail melanoma: a review of the clinicopathologic, dermoscopic, and genetic characteristics Nail melanoma is frequently diagnosed late because people and even some clinicians dismiss the band as a bruise or benign streak. The difference matters: melanoma caught while still in situ has an excellent prognosis, while advanced subungual melanoma can be devastating.
Glomus Tumors and Other Benign Growths
Not all lumps under a nail are cancerous. Glomus tumors are small, benign vascular growths that typically arise under the nail of a finger, causing intense, localized pain, cold sensitivity, and tenderness when the nail is pressed. The classic triad of symptoms is often enough for a clinical diagnosis without imaging.16PubMed Central. Subungual Glomus Tumours: Is Magnetic Resonance Imaging or Ultrasound Necessary for Diagnosis? When imaging is needed, MRI can pinpoint the tumor with high accuracy, showing a small, well-defined lesion that lights up brightly after contrast.17PubMed. Subungual glomus tumour: magnetic resonance imaging findings Treatment is surgical removal, and pain relief after excision is usually immediate and dramatic.
Other benign nail tumors include myxoid cysts (gel-filled bumps near the cuticle that can groove the nail plate), pyogenic granulomas (small, rapidly growing vascular nodules that bleed easily), and warts. High-frequency ultrasound has emerged as a useful tool for evaluating these growths, providing corrected or new diagnostic information in about a third of cases in one large series and influencing surgical planning across the board.18PubMed Central. High-Frequency Ultrasound Evaluation of the Nail Unit: Essential Insights for Clinicians
Drug-Induced Nail Changes
If you are undergoing cancer treatment and notice your nails darkening, thinning, lifting off the bed, or becoming painfully inflamed along the folds, the drugs are a likely culprit. Nail toxicity is one of the most common skin-related side effects of both traditional chemotherapy and newer targeted therapies.19PubMed Central. Narrative Review of Drug-Associated Nail Toxicities in Oncologic Patients Taxanes such as paclitaxel and docetaxel are particularly notorious, with all-grade nail changes reported in roughly a third to nearly half of patients receiving these drugs. EGFR inhibitors, used in several lung and colorectal cancers, frequently cause paronychia, a painful inflammation of the nail folds that can become infected and limit daily activities.20PubMed Central. Narrative Review of Drug-Associated Nail Toxicities in Oncologic Patients
These changes are almost never life-threatening, but they can significantly affect quality of life and sometimes lead to dose reductions or treatment delays. Keeping nails short, avoiding trauma, wearing gloves for wet work, and using nail-hardening agents can help. If paronychia develops, early treatment with antiseptic soaks and sometimes topical antibiotics or steroids can keep it from becoming severe enough to interrupt cancer therapy.
Self-Inflicted Nail Damage
Several common habits cause nail damage that mimics other diseases and can confuse even experienced clinicians. Nail biting (onychophagia) is the most familiar, often affecting multiple fingernails and leaving them short, ragged, and surrounded by torn cuticles. Nail picking (onychotillomania) involves using other nails or tools to pick, pull, or excessively manicure a nail, and in severe cases this can scar the matrix permanently, leading to irreversible nail loss.21PubMed. Nail tic disorders: Manifestations, pathogenesis and management
A subtler variant is habit-tic deformity. People with this condition repeatedly rub the cuticle of a thumbnail with an adjacent finger, often without realizing they are doing it. The result is a characteristic central groove running down the length of the thumbnail with horizontal ridges on either side, sometimes described as looking like a washboard. The key to treatment is making the person aware of the behavior, since many are genuinely surprised to learn they are causing the deformity themselves.22PubMed Central. Nail-Associated Body-Focused Repetitive Behaviors: Habit-Tic Nail Deformity, Onychophagia, and Onychotillomania Barrier methods like adhesive bandages over the cuticle and behavioral therapy can both help.
Lichen Planus, Trachyonychia, and Other Inflammatory Conditions
Lichen planus is an inflammatory condition that can affect the skin, mouth, and nails. When it targets the nails, it can cause thinning, ridging, splitting, and in its most destructive form, scarring that fuses the cuticle skin to the nail plate, a deformity called dorsal pterygium. In one retrospective study, dorsal pterygium was present in about 43% of patients at their first visit, meaning many people come in late after permanent damage has already started.23PubMed Central. Clinical features and treatment outcomes of nail lichen planus: A retrospective study Early treatment with potent topical or intralesional steroids can sometimes prevent this outcome, which is why any unexplained progressive thinning of multiple nails deserves dermatologic evaluation.
Trachyonychia, sometimes referred to as twenty-nail dystrophy, describes thin, brittle nails with excessive longitudinal ridging that gives them a sandpaper-like texture. It can affect all twenty nails, though the term has been loosely and sometimes incorrectly applied to other conditions that happen to involve multiple nails.24PubMed Central. Trachyonychia and Twenty-Nail Dystrophy: A Comprehensive Review and Discussion of Diagnostic Accuracy Trachyonychia can be seen in lichen planus, psoriasis, alopecia areata, and eczema. In children, it often improves spontaneously over years without aggressive treatment.
Cosmetic and Occupational Nail Damage
Not all nail disease comes from infection or internal conditions. The growing popularity of gel manicures, acrylic nails, and at-home nail art has brought a parallel rise in cosmetically induced nail problems. Aggressive filing to prepare the nail surface for acrylics can lead to “worn-down nail syndrome,” where the nail plate becomes dangerously thin from over-filing.25Skin Appendage Disorders. Adverse Effects of Do-It-Yourself Nail Cosmetics: A Literature Review The weakened nail is then more vulnerable to breaking, onycholysis, and secondary infection. Repeated exposure to the chemicals in acrylics and gel polish can also cause contact allergic reactions, both on the nails themselves and on the face and eyelids from touching.
Occupational exposure matters too. People who work with their hands in water for prolonged periods, such as healthcare workers, cleaners, bartenders, and hairdressers, are prone to chronic paronychia, where the cuticle seal breaks down and allows yeast and bacteria to colonize the nail folds. The resulting chronic inflammation causes the cuticle to retract and the nail to develop wavy, irregular ridges. The single most effective intervention is keeping the hands dry and rebuilding the cuticle barrier.
Nailfold Capillaroscopy in Connective Tissue Disease
One of the more specialized uses of nail examination has nothing to do with the nail plate at all. In nailfold capillaroscopy, a clinician uses a magnifying device to examine the tiny blood vessels visible through the skin at the base of the fingernail. The pattern of these capillaries can help diagnose and monitor autoimmune diseases like systemic sclerosis (scleroderma) and dermatomyositis. Abnormal patterns, including enlarged or giant capillaries, hemorrhages, and areas where capillaries have dropped out entirely, are well established in systemic sclerosis and have been found in other connective tissue diseases including myositis, even in patients without Raynaud’s phenomenon.26PubMed Central. Nailfold capillaroscopy in myositis: A case series
A comparison of capillaroscopy findings in dermatomyositis and systemic sclerosis found that while both conditions produce abnormal patterns, the specific features differ. Patients with dermatomyositis tend to show more abnormally branching capillaries, a sign of active new vessel formation, whereas systemic sclerosis patients show more giant capillaries and hemorrhages.27PubMed. Long-term follow-up of nailfold videocapillaroscopic changes in dermatomyositis versus systemic sclerosis patients Interestingly, the capillaroscopic changes in dermatomyositis remained stable over long-term follow-up, in contrast to the progressive worsening typically seen in systemic sclerosis.28PubMed. Long-term follow-up of nailfold videocapillaroscopic changes in dermatomyositis versus systemic sclerosis patients This means the technique is useful not just for initial diagnosis but for tracking disease behavior over time.