Ridged Nails: What Could Be Causing It

Vertical vs. Horizontal: The Direction Tells the Story

The orientation of nail ridges separates the benign from the potentially serious. Vertical ridges, called longitudinal ridging or onychorrhexis, run from the cuticle to the free edge and become more prominent with age. A 2022 review in the Journal of the European Academy of Dermatology and Venereology reported that longitudinal ridging appears in up to 85% of individuals older than 65 [1]. These ridges reflect a gradual thinning of the nail plate and reduced blood flow to the nail matrix over decades.

Horizontal ridges tell a completely different story. Named Beau's lines after the French physician Joseph Honoré Simon Beau, who first described them in 1846, these transverse depressions form when the nail matrix temporarily stops producing cells [2]. The depth of the groove correlates with the severity and duration of the insult. A shallow line might follow a high fever lasting two days. A deep groove can indicate prolonged chemotherapy or severe malnutrition. Because fingernails grow at roughly 3.5 mm per month, the distance between the groove and the proximal nail fold provides a rough timeline of when the disruption occurred [3].

Not all ridges fit neatly into one category. Some conditions produce both longitudinal and transverse changes. Psoriatic nail disease, for instance, can cause pitting, ridging in multiple directions, and onycholysis simultaneously.

Aging and Normal Wear

Aging is the single most common reason for ridged nails. It does not require treatment. The nail matrix, like other tissues, loses regenerative capacity over time. Cell turnover slows. The nail plate becomes thinner, more brittle, and develops fine longitudinal striations that catch light at certain angles.

A study published in the British Journal of Dermatology measuring nail plate thickness in 200 healthy subjects found a statistically significant decrease in thickness after age 50 (mean reduction 0.12 mm, P<0.01) [4]. This thinning makes pre-existing ridges more visible, creating the impression that ridges appeared suddenly when they actually developed gradually.

Dr. Antonella Tosti, a professor of dermatology at the University of Miami and one of the foremost authorities on nail disorders, has written: "Longitudinal ridging is the nail equivalent of wrinkles on the skin. It is a physiological change that does not warrant investigation in the absence of other nail or systemic signs" [5].

Dehydration accelerates the appearance of ridges. Frequent handwashing, exposure to acetone-based nail polish removers, and low ambient humidity strip moisture from the nail plate.

Nutritional Deficiencies That Affect Nail Growth

Iron deficiency is the most extensively documented nutritional cause of nail changes. The classic finding is koilonychia (spoon-shaped nails), but ridging and brittleness often precede the full spoon deformity. The World Health Organization estimates that iron deficiency affects approximately 2 billion people globally [6]. In a cross-sectional study of 150 patients with iron deficiency anemia, 42% exhibited some form of nail dystrophy, including longitudinal ridging, before hemoglobin dropped below 10 g/dL [7].

Zinc deficiency produces nail changes too. White spots (leukonychia punctata) get most of the attention, but Beau's lines and generalized ridging also occur with prolonged zinc depletion. Patients on long-term proton pump inhibitors are at elevated risk because gastric acid is required for optimal zinc absorption [8].

Biotin has received outsized attention in consumer media. The evidence supporting biotin supplementation for nail ridging is limited. A small, uncontrolled trial of 45 patients with brittle nails showed improvement in nail firmness after 5.5 months of 2.5 mg daily biotin, but the study lacked a placebo arm and blinding [9]. The American Academy of Dermatology does not include biotin in its formal treatment guidelines for nail disorders [10].

Other nutrients linked to nail changes include vitamin B12, folate, and protein. Severe caloric restriction, as seen in anorexia nervosa, produces Beau's lines because the nail matrix prioritizes survival over growth.

Thyroid Disease and Endocrine Disruption

Both hypothyroidism and hyperthyroidism alter nail architecture. Hypothyroidism slows cell turnover throughout the body, including the nail matrix. Nails become dry, thick, and ridged. They may also develop a yellowish discoloration. Hyperthyroidism accelerates growth but produces a soft, fragile plate prone to onycholysis (separation from the nail bed).

A retrospective analysis of 300 patients with autoimmune thyroid disease found nail abnormalities in 56% of hypothyroid patients and 38% of hyperthyroid patients [11]. Ridging was the most common finding in the hypothyroid group (present in 31% of cases), followed by brittleness and slow growth.

The Endocrine Society's 2023 clinical practice guideline on hypothyroidism notes that nail and hair changes are among the earliest clinical signs of subclinical hypothyroidism, sometimes appearing before TSH rises above the standard reference range of 4.5 mIU/L [12]. Thyroid function testing (TSH with reflex free T4) is a reasonable first laboratory step when a patient presents with new-onset nail ridging alongside fatigue, weight changes, or hair thinning.

Diabetes mellitus affects nails through microvascular compromise. Poor perfusion to the digit tips slows nail matrix function. A study in Diabetes Care documented nail abnormalities in 46.5% of 214 diabetic patients compared to 22.9% of age-matched controls [13].

Dermatologic Conditions

Several skin diseases target the nail unit directly. Psoriasis is the most common. Nail involvement occurs in approximately 50% of patients with cutaneous psoriasis and up to 80% of those with psoriatic arthritis [14]. Pitting (small, ice-pick depressions) is the hallmark, but ridging, crumbling, and subungual hyperkeratosis also occur.

Lichen planus affects nails in about 10% of cases and can cause permanent scarring of the nail matrix if untreated [15]. The ridging pattern in lichen planus tends to produce prominent longitudinal grooves, sometimes with thinning so severe that the nail splits (onychoschizia). Early recognition matters because topical or intralesional corticosteroids can prevent irreversible damage.

Alopecia areata, an autoimmune condition primarily known for hair loss, causes nail pitting and ridging in 10% to 66% of affected individuals depending on disease severity [16]. The nail pitting in alopecia areata tends to be geometric and arranged in a grid pattern, distinguishing it from the random pitting of psoriasis.

Fungal nail infection (onychomycosis) can mimic ridging but typically produces thickening, discoloration, and debris under the nail rather than clean longitudinal lines. KOH preparation or fungal culture confirms the diagnosis when clinical distinction is unclear.

Systemic Illness and Medication Effects

Beau's lines serve as a medical timeline etched into the nail plate. Any illness severe enough to temporarily suppress cell division in the nail matrix can produce them. Documented causes include high fevers from pneumonia or influenza, myocardial infarction, major surgery, and severe emotional stress [17].

Chemotherapy is a well-known trigger. Cytotoxic drugs interrupt the rapidly dividing cells of the nail matrix just as they interrupt tumor cells. A prospective study of 53 patients receiving taxane-based chemotherapy found Beau's lines in 73.6% of patients within three cycles [18]. The lines appeared on all 20 nails simultaneously, a pattern that strongly suggests a systemic rather than local cause.

The COVID-19 pandemic introduced clinicians to a related phenomenon. Reports in the British Journal of Dermatology described Beau's lines appearing 3 to 4 weeks after acute SARS-CoV-2 infection, consistent with the expected nail growth delay [19]. Some patients developed red lunulae (half-moon discoloration at the nail base) alongside the ridging.

Medications beyond chemotherapy can also cause nail changes. Retinoids (isotretinoin, acitretin) produce nail fragility and ridging in a dose-dependent fashion. Antiretroviral drugs, particularly zidovudine, cause characteristic nail hyperpigmentation with ridging.

How Ridged Nails Are Diagnosed

Diagnosis begins with a careful history and physical examination. The clinician asks about the timeline of onset, whether all nails or only certain nails are affected, associated symptoms (skin rash, hair loss, fatigue, weight change), medication use, and dietary habits.

Dermatoscopy (examination with a handheld polarized light magnifier) allows visualization of the nail plate surface at 10x magnification. This tool can distinguish between normal age-related ridging, pitting, and early signs of lichen planus or psoriasis without biopsy [20].

Laboratory workup, when indicated, typically includes a complete blood count, ferritin, TSH, free T4, zinc, vitamin B12, and a comprehensive metabolic panel. The American Academy of Dermatology recommends reserving laboratory testing for patients with horizontal ridging, ridging affecting multiple nails simultaneously, or ridging accompanied by other systemic symptoms [10].

Dr. Ralph Daniel, a clinical professor of dermatology at the University of Mississippi Medical Center, has stated: "The nail is a window into systemic health. A single ridged thumbnail in a 70-year-old is almost never pathologic. Beau's lines on all 20 nails in a 35-year-old demand a workup" [21].

Nail biopsy is the gold standard for definitive diagnosis but is rarely necessary. It is reserved for cases where malignancy is suspected (e.g., a single dark longitudinal band that could represent subungual melanoma) or when inflammatory nail disease fails to respond to empiric treatment.

Treatment Approaches by Cause

Treatment depends entirely on the underlying etiology. There is no universal "ridge fixer."

For age-related vertical ridging, management is cosmetic. Gentle buffing with a fine-grit nail file can reduce the visual prominence of ridges. Ridge-filling base coats provide a smooth surface. Moisturizing the nail plate and cuticle with petrolatum or a urea-based cream (10% to 20% urea) improves hydration and reduces brittleness [22].

For iron deficiency, oral ferrous sulfate 325 mg daily (providing 65 mg of elemental iron) taken with vitamin C to enhance absorption is standard therapy. Nail improvement lags behind laboratory improvement by 3 to 6 months because the entire nail plate must regrow [23].

For thyroid-related changes, thyroid hormone replacement (levothyroxine) at the appropriate dose corrects nail abnormalities over 6 to 12 months. The nails are among the last clinical features to normalize because growth is slow.

For psoriatic nail disease, treatment options include topical corticosteroids (clobetasol 0.05% applied to the nail fold), topical calcipotriol, intralesional triamcinolone acetonide (2.5 to 5 mg/mL injected into the proximal nail fold), and systemic therapies for severe cases. Biologic agents targeting TNF-alpha and IL-17 have shown significant nail psoriasis improvement in clinical trials. The TRANSFIGURE trial of secukinumab 300 mg demonstrated a 63.6% mean improvement in NAPSI (Nail Psoriasis Severity Index) score at week 32 compared to 10.8% for placebo [24].

For lichen planus of the nail, early treatment with intralesional triamcinolone (5 mg/mL every 4 to 6 weeks for 3 to 6 sessions) can prevent permanent nail loss. Systemic options include oral prednisone tapers, hydroxychloroquine, and mycophenolate mofetil for recalcitrant disease [15].

For Beau's lines caused by acute illness, no treatment is needed beyond addressing the underlying condition. The lines grow out with the nail and disappear within 6 to 9 months for fingernails and 12 to 18 months for toenails.

When to Seek Medical Evaluation

Most nail ridging does not require a doctor visit. Vertical ridges that develop gradually after age 40, affect multiple nails symmetrically, and occur without other symptoms fall squarely within normal aging.

Seek evaluation if any of the following are present: horizontal ridges on multiple nails, a single dark band running lengthwise (rule out melanoma), ridging accompanied by nail separation from the bed, ridging with significant hair loss or skin rash, or ridging developing rapidly in someone under 30.

A referral to dermatology is appropriate when the primary care evaluation is inconclusive or when inflammatory nail disease requires intralesional injection or biopsy. Patients with suspected psoriatic nail disease should be screened for joint symptoms, as nail involvement in psoriasis is a predictor of future psoriatic arthritis. A 2019 meta-analysis in Rheumatology found that nail dystrophy carried an odds ratio of 2.93 (95% CI 1.68 to 5.12) for developing psoriatic arthritis [25].