What causes horizontal lines on toenails?

Horizontal lines on toenails — called Beau's lines — are caused by temporary interruptions in nail growth. Common causes include serious illness, high fever, nutritional deficiency, chemotherapy, major surgery, or severe physical stress. The lines appear across all nails at roughly the same position.

Are horizontal toenail lines a sign of something serious?

Beau's lines can sometimes indicate a serious underlying health event that occurred several months ago (nails grow slowly). If horizontal lines appear without an obvious cause like illness or injury, it's worth checking with your doctor to rule out systemic conditions such as diabetes, thyroid disease, or nutritional deficiency.

Do horizontal toenail lines go away?

Yes — Beau's lines grow out as the nail grows and typically resolve on their own once the underlying cause is addressed. Toenails grow about 1–2mm per month, so lines may take 6–12 months to fully grow out. No specific treatment is needed for the lines themselves.

When should I see a podiatrist?

For persistent foot/ankle pain, difficulty walking, numbness, non-healing wounds, skin changes, or deformities. Dr. Biernacki offers same-day appointments. Call 810-206-1402.

Does Dr. Biernacki accept insurance?

Balance Foot & Ankle accepts most major plans including BCBS, Aetna, United, Cigna & Medicare. Call 810-206-1402 to verify coverage. Affordable self-pay options available.

What to expect at your first podiatry visit?

Comprehensive evaluation including history, exam, biomechanical assessment, and in-office X-rays. Same-day diagnosis and treatment when possible. Most visits take 30-45 minutes.

What causes thick, discolored toenails?

Thick, yellow-brown, or brittle toenails are most commonly caused by fungal infection (onychomycosis), affecting 10–14% of the population. Other causes include psoriasis, repeated microtrauma from tight shoes, peripheral vascular disease, and age-related changes. A podiatrist can clip a nail sample for lab analysis to confirm the diagnosis before recommending treatment.

How are ingrown toenails treated?

Mild ingrown toenails can sometimes be managed at home by soaking twice daily and placing a small piece of cotton under the corner. If there is pus, significant swelling, or the corner is deeply embedded, see a podiatrist. In-office treatment involves local anesthesia and removal of the offending nail border. For recurrent ingrown nails, phenol matrixectomy permanently prevents regrowth of that nail edge.

Can toenail changes be a sign of a systemic disease?

Yes. Nail pitting and separation suggest psoriasis; spoon-shaped nails suggest iron-deficiency anemia; yellow nails may indicate lymphedema or rheumatoid arthritis; splinter hemorrhages can indicate infective endocarditis. Diabetic patients frequently develop nail thickening from microtrauma and circulation changes. Podiatrists examine nails at every visit with systemic conditions in mind.

When should I see a podiatrist for a toenail problem?

See a podiatrist if a toenail is painful, infected, has changed color or thickness over months, is growing into the skin, or if you have diabetes and notice any nail change. Diabetic patients should never cut ingrown or thickened nails at home. Balance Foot & Ankle provides nail care in Howell and Bloomfield Hills — call (810) 206-1402.

What causes horizontal lines on toenails?

The most common causes are superficial and cosmetic: nail polish damage, acetone overuse causing surface dehydration, onychorrhexis (brittle nails with shallow horizontal cracking), and minor repetitive trauma from shoes or activity. The clinically important cause is Beau's lines — deep transverse grooves that span the full nail plate and indicate a temporary arrest in nail matrix cell division during a systemic illness, major surgery, high fever, or severe nutritional stress. Beau's lines can date the onset of an illness based on their position on the nail.

What are Beau's lines and should I be worried?

Beau's lines are deep, transverse furrows that encircle the full nail plate. They represent a period when nail matrix cell division temporarily stopped — caused by systemic illness (COVID-19, pneumonia, sepsis), major surgery, severe nutritional deficiency, or high-dose chemotherapy. They are not dangerous in themselves but are a record of a physiologic event. If Beau's lines appear on all nails simultaneously, they point to a systemic cause. If they appear on only one nail, local trauma or repeated pressure is more likely. They require evaluation only if the underlying systemic cause is unknown or ongoing.

How do I tell the difference between Beau's lines and nail polish damage?

Nail polish damage and acetone-related lines are superficial, patchy, and typically limited to nail surfaces that were exposed to repeated polish application and removal. They do not create a deep groove that can be felt by running a fingernail across the surface. Beau's lines are deep enough to create a physical groove across the full width of the nail. They also tend to appear simultaneously across multiple nails and at approximately the same distance from the cuticle on each nail — corresponding to the same time period when the systemic event occurred.

Do horizontal lines on toenails go away on their own?

Yes — all horizontal lines on toenails grow out with the nail plate over time. Toenails grow approximately 1.5–2 mm per month, so a line near the cuticle takes 6–12 months to fully grow out. Surface lines from nail polish or minor damage may respond to rehydration and a break from nail products. Beau's lines will grow out naturally once the underlying systemic cause resolves — they do not require any nail treatment directly.

Horizontal Ridges on Toenails: Causes & Treatment

Medically reviewed by Dr. Tom Biernacki, DPM

Board-certified podiatric surgeon | Balance Foot & Ankle
Last reviewed: May 2026

MICHIGAN PODIATRIST INSIGHT

Horizontal lines on toenails hinge on a single clinical feature: whether the groove circles the entire nail plate uniformly, or appears only on part of it. Patchy, superficial, or nail-polish-related lines are almost always cosmetic. But a deep indented groove spanning the full width of every nail — appearing after an illness, surgery, or period of severe physiologic stress — is a Beau's line: a recorded systemic event embedded in keratin. The two look similar but require completely different responses. Call (810) 206-1402 if you're not sure which you're looking at.

Horizontal Lines on Toenails: Normal vs. Not Normal

Noticing horizontal lines running across your toenails is surprisingly common, and for most people it is completely harmless. The concern usually comes from reading that horizontal toenail lines might mean serious illness — which is sometimes true, but much less often than the internet suggests. In our Howell and Bloomfield Hills podiatry offices, the majority of patients who come in worried about horizontal toenail lines leave reassured that their nails are showing normal wear, cosmetic damage, or minor trauma patterns, not systemic disease.

Here is how to read your own nail lines and decide whether you need clinical evaluation or just better nail care.

The Quick Diagnostic Test: Superficial or Deep?

Before worrying about causes, answer this question: can you feel the lines when you run your fingernail across the surface of the toenail?

Superficial lines (barely visible, hard to feel): Almost certainly cosmetic — nail polish damage, surface dryness, mild trauma. No medical evaluation needed unless other symptoms present.
Moderate lines (visible, slightly felt): Could be cosmetic or could be onychorrhexis (brittle nail condition). Watch and treat with nail care. Evaluate if persistent or worsening.
Deep grooves (clearly indented, cross the full width of the nail): These are likely Beau’s lines — read our dedicated Beau’s lines guide for a full explanation of systemic causes and when to see a doctor.

Key takeaway: If the lines are patchy, vary between nails, or appeared gradually over time, they’re almost always cosmetic. If a uniform deep groove appeared on all nails at roughly the same time (suggesting a single systemic event), that is a Beau’s line pattern worth evaluating.

Cause #1: Nail Polish and Acetone Damage

The most common cause of horizontal lines on toenails in our patients — especially women who regularly wear nail polish — is damage from nail products. This can happen in several ways:

Acetone-Based Nail Polish Remover

Acetone is a powerful solvent that strips natural oils from the nail plate, leaving it dehydrated and brittle. With repeated use, the nail plate develops microscopic horizontal fractures within its laminar structure. These appear as superficial horizontal lines or a finely ridged texture across the nail. The lines typically run parallel across multiple nails that have been similarly treated.

Fix: Switch to acetone-free nail polish remover. Allow nails to breathe between polish applications. Apply nail strengthener or cuticle oil (jojoba, vitamin E) daily to rehydrate the nail plate. Lines will grow out over 6-9 months as the nail plate renews.

Keratin Granulations from Nail Polish

Keratin granulations are rough, chalky white or opaque patches on the nail surface that appear when nail polish is removed — particularly after long-wear polish or gel polish. The surface layers of keratin are stripped away with the polish, creating a rough, irregular texture with horizontal striations. This is a very common and completely benign condition, though it looks alarming. For a full explanation, see our dedicated keratin granulations guide.

Keratin granulations are a well-documented result of prolonged nail polish use. The American Academy of Dermatology recommends allowing nails to rest between polish applications to prevent this superficial damage.

Gel and Acrylic Polish Trauma

Aggressive buffing during gel polish application, improper removal (peeling rather than soaking off), or repeated filing of the nail surface creates horizontal surface trauma visible as fine lines across the nail. If you feel your nail has become noticeably thinner, softer, or more flexible after extended gel polish use, this is nail plate thinning — a real condition that warrants a break from all nail products.

Cause #2: Onychorrhexis (Brittle Nails with Horizontal Lines)

Onychorrhexis is a nail dystrophy characterized by brittleness and a tendency to split or fracture horizontally. Unlike the longitudinal ridges of onychoschizia (which run along the length of the nail), onychorrhexis produces a rough, ridged surface texture across the width of the nail plate.

Causes of onychorrhexis:

Repeated wetting and drying (common in healthcare workers, dishwashers, swimmers)
Iron deficiency — one of the most common and correctable causes
Hypothyroidism — the thyroid hormone regulates nail growth and protein synthesis
Excessive use of drying nail products
Aging — the nail plate naturally loses moisture with age
Biotin deficiency (though evidence for supplementation is modest in most people)

Treatment: Address the underlying cause. For structural support, daily application of a nail hardener (ideally formaldehyde-free) and a rich cuticle oil. Keep nails slightly longer to reduce mechanical stress. Wear gloves for wet work. If iron or thyroid issues are suspected, a simple blood panel (ferritin, TSH) can rule them in or out.

Cause #3: Minor Trauma — Shoes and Everyday Life

The toenails take more mechanical abuse than people realize. Every step you take creates a small compressive force through the nail plate. Over time — particularly in shoes that are slightly too short, or during athletic activities — cumulative microtrauma to the nail matrix creates horizontal surface irregularities.

Repetitive microtrauma (runner’s toe): Long-distance runners and hikers frequently develop horizontal surface lines on the great toenail from repeated impact against the shoe toe box. If the shoe fits, this is simply cosmetic and doesn’t require treatment.
Toe-box compression: Shoes too narrow for the foot compress the lateral toenails (4th and 5th) creating surface stress lines over months to years.
A single acute injury: Dropping something on a toe or stubbing it hard can temporarily interrupt nail matrix activity at that moment, leaving a horizontal groove that slowly grows out.

Key takeaway: A single horizontal groove on ONE toenail that appeared after a specific injury or trauma is almost always that injury’s growth record. It will grow out over 6-9 months. No treatment needed unless it causes structural weakness or pain.

Cause #4: Normal Aging of the Nail Plate

Toenail structure changes significantly with age. The nail plate thickens, becomes more brittle, grows more slowly, and develops surface irregularities including horizontal texture changes that reflect decades of cumulative minor stress. In adults over 60, some degree of horizontal surface ridging is essentially universal and represents normal nail aging, not disease.

What differentiates normal aging ridges from Beau’s lines: aging ridges develop gradually over years, are present consistently across all nails as a background texture, and don’t appear suddenly. Beau’s lines appear as distinct groove events — a clearly defined groove that wasn’t there before, often affecting all nails simultaneously.

Cause #5: Fungal Nail Infection (Onychomycosis)

Advanced fungal nail infection can disrupt the nail plate structure producing horizontal bands of discoloration and surface irregularity alongside the more typical thickening and yellowing. The distinction from purely cosmetic lines: fungal lines are usually accompanied by nail plate thickening, yellow-white-brown discoloration, nail separation from the bed (onycholysis), and crumbly texture at the nail edges.

If your horizontal lines are accompanied by any of these changes, see our guide to thick yellow toenails and consider a nail clipping test to rule out fungal infection before treating cosmetically.

When Horizontal Lines Mean Something More: Beau’s Lines

Beau’s lines are the clinically important form of horizontal toenail lines — deep grooves that circle the nail plate, representing a pause in nail matrix growth during a significant physiological stress. They are named after the 19th-century French physician Joseph Honore Simon Beau who first described them systematically.

Beau’s lines are clinically distinct from other horizontal toenail markings — for a complete breakdown of causes and treatment timelines, see our detailed guide to horizontal ridges on toenails.

The key features that distinguish Beau’s lines from cosmetic lines:

Deep indentation (groove crosses the full thickness of the visible nail)
Affects multiple or all nails at the same relative position (same distance from the cuticle = same time of formation)
Appeared after a discrete health event: severe illness, major surgery, chemotherapy, high fever, significant nutritional disruption
There is often a clear “before and after” — the nail was normal, then this appeared

For a complete guide to Beau’s lines — including the conditions they’re associated with, how to date when the stress occurred, and when to seek evaluation — see our dedicated article: Horizontal Ridges on Toenails: What Beau’s Lines Mean.

⚠️ See a podiatrist or your doctor if your horizontal lines:

Are deep grooves that appeared on multiple nails at the same time without an obvious cosmetic or trauma cause
Are accompanied by nail thickening, yellowing, or crumbling (possible fungal infection)
Are combined with systemic symptoms: fatigue, hair loss, weight changes, or recent significant illness
Have been worsening despite stopping all nail products and implementing nail care
Are on a diabetic patient’s foot — any nail change warrants professional evaluation

How to Improve Cosmetic Horizontal Lines on Toenails

For the majority of horizontal lines that are confirmed cosmetic, a consistent nail care routine produces meaningful improvement over 6-9 months as the damaged nail plate grows out.

Daily cuticle oil: Jojoba, argan, or vitamin E oil massaged into the cuticle and nail plate daily replenishes the lipid layer that holds moisture in the nail plate. This is the single most impactful nail care habit.
Nail hardener (formaldehyde-free): Applied 2x/week fills surface irregularities and provides a structural scaffold while the nail grows out.
Hydrating nail polish base coat: If you use nail polish regularly, a hydrating base coat (containing ingredients like hyaluronic acid, peptides, or calcium) reduces the drying and adhesion damage of regular polish use.
Acetone-free remover exclusively: EthylAcetate-based removers are gentler and preserve nail plate lipids better than acetone.
Biotin supplement (2,500-5,000 mcg/day): Evidence is modest, but multiple small trials show improved nail brittleness with biotin supplementation over 6 months in people with documented brittle nails.
Protein and iron adequacy: Nails are made of keratin protein. A diet inadequate in protein or iron will produce weak, ridged nails regardless of topical care. Check ferritin if nail quality doesn’t improve with topical care.

Frequently Asked Questions

Are horizontal lines on toenails normal?

Superficial horizontal lines from nail products, aging, or minor trauma are extremely common and normal. Deep grooves that appeared suddenly on multiple nails simultaneously (Beau’s lines) are less common and worth evaluating. If you’re unsure which you have, the quick test is whether the lines can be felt as a definite groove and whether all nails were affected at once.

How long does it take for horizontal lines on toenails to grow out?

Toenails grow approximately 1.5 mm per month. A full toenail is roughly 10-14 mm long from the cuticle to the free edge. A horizontal line at the cuticle will take 6-9 months to grow out completely. Lines closer to the free edge of the nail when first noticed will grow out faster. During this time, nail oil and strengthener keep the growing nail from splitting along the existing line.

Can nail polish cause horizontal lines on toenails?

Yes — regular nail polish, particularly when removed with acetone-based remover or when gel polish is peeled off rather than properly soaked, dehydrates and mechanically damages the nail plate. Keratin granulations (white chalky horizontal patches) and fine surface ridging are direct results of this damage. The solution is switching to gentler products, allowing regular polish-free periods, and actively rehydrating the nail plate.

What vitamin deficiency causes horizontal lines on nails?

Iron deficiency is the most common nutritional cause of brittle, horizontally lined nails — low ferritin levels impair the oxygen delivery needed for robust nail matrix cell production. Zinc deficiency can cause Beau’s line-type grooves (Beau’s lines have been reported in acute zinc deficiency). Protein deficiency reduces the substrate for keratin synthesis. Biotin deficiency is often cited but is actually rare in people eating normally; supplementation helps mainly in people with confirmed deficiency.

The Bottom Line

Most horizontal lines on toenails are cosmetic — the product of nail polish habits, minor trauma, dryness, or normal aging — and will improve with consistent nail care over 6-9 months. The important exception is deep, uniform grooves across all nails that appeared after a systemic stress event (Beau’s lines), which are worth evaluating by a physician. When in doubt, our podiatry office can assess your nail changes in a single appointment and give you a clear answer.

Sources

Haneke E. “Nail diseases in clinical practice.” Skin Appendage Disorders. 2024.
Iorizzo M, et al. “Brittle nails.” Journal of the American Academy of Dermatology. 2023.
Piraccini BM, Alessandrini A. “Drug-related nail disease.” Clinics in Dermatology. 2025.

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For a complete guide to toenail conditions and treatment options, see our Toenail Fungus & Nail Condition Treatment Guide.

What causes horizontal lines (Beau’s lines) on toenails?

Beau’s lines form when nail growth temporarily stops during a systemic illness, high fever, nutritional deficiency, chemotherapy, or severe physical stress. The nail matrix pauses production, leaving a groove that grows out over 6–9 months.

Are Beau’s lines serious?

Multiple simultaneous Beau’s lines across all nails suggest a significant systemic event and warrant medical evaluation. A single line on one nail is usually caused by local trauma or a mild illness and resolves on its own.

How long does it take Beau’s lines to grow out?

Toenails grow approximately 1.5 mm per month. A Beau’s line near the base of a toenail takes roughly 12–18 months to reach the tip and grow off the nail completely.

📋 Dr. Tom Biernacki, DPM, FACFAS answers:

Horizontal lines on toenails can be completely normal or indicate a systemic health event. Beau’s lines — deep transverse grooves — form when nail growth temporarily stops due to illness, high fever, surgery, or severe nutritional stress; their position on the nail tells you roughly when the event occurred (nails grow about 3mm per month). Mees’ lines are white horizontal bands historically linked to arsenic poisoning but also seen in kidney disease. Trauma lines from repetitive shoe pressure are usually confined to one or two nails and appear on the same nail repeatedly. Single, shallow lines that appeared after a cold or the flu and are growing out with the nail don’t require any treatment. Multiple lines on all nails that appeared suddenly should prompt evaluation for a systemic cause.

Dr. Tom Biernacki, DPM

Dr. Tom Biernacki, DPM is a board-certified foot & ankle surgeon (ABFAS & ABPM) at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has made him one of the most-followed foot & ankle educators on YouTube.