Quick answer: Horizontal ridges or dents across a toenail (Beau’s lines) appear when nail growth briefly pauses — often after illness, an injury to the nail, or significant physical stress. A single ridge usually grows out over several months; multiple, recurring, or discolored ridges should be checked by a podiatrist.
Podiatrist’s Answer
Horizontal ridges — called Beau’s lines — form when nail growth temporarily stops due to a systemic stressor: high fever, surgery, chemotherapy, severe illness, or nutritional deficiency. A single ridge that grows out is usually benign. Multiple parallel ridges or ridges that don’t grow out warrant lab work to rule out thyroid disease or zinc deficiency.
— Dr. Tom Biernacki, DPM, Board-Certified Podiatric Surgeon, Balance Foot & Ankle
A single horizontal dent or groove across your toenail isn’t aging — it’s called a Beau’s line, and your body is essentially leaving you a 3-month-old receipt of something it went through (illness, stress, fever, even a medication change). After examining well over 15,000 toenails in my Michigan podiatry practice, here’s exactly what horizontal ridges and dents in toenails mean in 2026, when they’re harmless, and the four patterns that warrant a same-week appointment.
Horizontal ridges look like one condition — but our podiatrists have identified 4 distinct ridge patterns with completely different causes and urgency levels. The pattern most patients dismiss as “just aging” is the one we most need to see in office. If yours appeared suddenly after a stressful event or you have more than 3 nails affected, call (810) 206-1402 — same-week appointments in Howell & Bloomfield Hills.
Board-certified podiatric surgeon | Balance Foot & Ankle
Last reviewed: May 2026
You look at your toenails and notice a groove — or several grooves — running side-to-side across the nail, like rings in a tree trunk. They were not there before. The nail looks otherwise normal, but those indentations are clearly something new.
In our clinic, horizontal ridges are one of the more diagnostically interesting nail findings we encounter, because they function as a timeline. Each groove represents a specific moment when the nail matrix — the tissue that manufactures the nail — hit pause. Understanding what caused that pause is the key to understanding what these lines mean for your health.
Most Common Mistake
Treating Beau’s lines with antifungal cream. Most patients assume horizontal ridges mean nail fungus and spend months applying OTC antifungal products — which do nothing for Beau’s lines because these are structural grooves from growth arrest, not an infection. The fix is identifying the underlying systemic trigger (illness, nutritional gap, medication), not antifungals. If the nail is also yellowing or thickening, see a podiatrist to confirm the diagnosis before treating.
What Are Beau’s Lines?
Beau’s lines are transverse (side-to-side) depressions or ridges in the nail plate, named after French physician Joseph Honore Simon Beau, who described them in 1846. They form when the nail matrix — the crescent of tissue beneath the proximal nail fold at the nail base — temporarily reduces or stops its normal production of nail cells.
The nail plate is manufactured continuously, advancing forward at approximately 1.5-2 mm per month for toenails. When matrix activity is disrupted, the emerging nail is thinner at that point, creating a transverse groove. The nail does not “know” it was disrupted — it simply records the event in its structure, much like a tree ring records a drought year. When the stressor resolves, normal production resumes and the groove grows forward toward the free edge.
This growth timeline means you can estimate when the disruption occurred. Measure the distance from the proximal nail fold (the base of the nail) to the center of the groove, then divide by the growth rate. A Beau’s line located 5 mm from the base of the great toenail occurred approximately 2-3 months ago. A line at 10 mm occurred 5-6 months ago. This dating is approximate but clinically useful.
Key takeaway: Beau’s lines are a timeline of past stressors. The position of the groove on the nail tells you roughly when the disruption occurred. A line at 5mm from base = approximately 2-3 months ago; at 10mm = 5-6 months ago.
What Causes Horizontal Ridges on Toenails?
Noticed ridges, dents, or unusual changes in your toenails?
Board-certified podiatric surgeons — same-week appointments in Howell & Bloomfield Hills, MI. Most insurance accepted.
Book an Appointment → ☎ (810) 206-1402Any physiological stress significant enough to temporarily suppress the nail matrix can produce Beau’s lines. The causes fall into several categories:
Acute systemic illness: High fever (above 39 degrees Celsius / 102 Fahrenheit), severe infections (pneumonia, COVID-19, sepsis), major surgery, and childbirth are among the most common causes. In our practice, we frequently see patients with Beau’s lines appearing 2-3 months after a major illness — the timing lines up perfectly with the nail growth math. COVID-19 in particular has been associated with prominent Beau’s lines observed at 1-3 months post-infection.
Nutritional deficiencies: Severe protein deficiency (hypoalbuminemia), zinc deficiency, and iron deficiency anemia can all produce Beau’s lines. Unlike leukonychia (white spots), which is usually benign, Beau’s lines are more reliably associated with genuine nutritional compromise. A full blood panel — albumin, zinc, iron studies, CBC — is reasonable if you have multiple deep Beau’s lines without an obvious past illness to explain them.
Chemotherapy: Many cytotoxic agents suppress rapidly dividing cells, including the nail matrix. Beau’s lines appearing predictably after chemotherapy cycles are a well-documented phenomenon. Paclitaxel, docetaxel, and fluorouracil are among the most commonly implicated agents.
Local trauma or nail procedure: A significant injury to the nail matrix area, aggressive nail surgery, or even very tight footwear causing chronic pressure on the matrix can produce localized Beau’s lines affecting one nail rather than all nails simultaneously.
Chronic systemic diseases: Peripheral vascular disease, Raynaud’s phenomenon, hypothyroidism, diabetes with poor glycemic control, and psoriasis affecting the nail matrix can all produce Beau’s lines — often multiple lines or continuous, irregular ridging reflecting ongoing matrix disruption rather than a single past event.
Key takeaway: A single Beau’s line on all nails simultaneously = a past systemic event (illness, surgery, fever). Multiple lines, lines progressing over months, or lines on only one nail = warrants evaluation for ongoing systemic disease, deficiency, or local cause.
Beau’s Lines vs. Other Toenail Ridges
Not all toenail ridges are Beau’s lines. The pattern and orientation of ridges carry distinct diagnostic meaning, and it is worth knowing the differences before assuming the worst.
Vertical (longitudinal) ridges: Fine lines running from the nail base to the tip, parallel to the long axis of the nail. These are almost universally benign and increase with age — they reflect the normal aging process of the nail matrix, similar to how skin develops fine lines over time. Longitudinal ridges are extremely common after age 50 and are not a cause for concern in the absence of other nail changes. These are the most common nail changes we see and the most commonly confused with Beau’s lines by patients.
Mees’ lines: Transverse white bands running across the full nail width — these differ from Beau’s lines in that Mees’ lines are a white discoloration within the nail plate, not a physical indentation. Mees’ lines are associated with arsenic poisoning, thallium toxicity, renal failure, and rarely, certain medications. Running a fingernail across the nail: Beau’s lines create a physical groove you can feel; Mees’ lines are flush with the nail surface.
Onychorrhexis: Multiple fine, irregular longitudinal ridges giving the nail a “corrugated tin” appearance. Associated with aging, trauma, lichen planus, and sometimes rheumatoid arthritis. Distinctly different from Beau’s lines — longitudinal, not transverse.
Onychoschisis: Horizontal splitting of the nail plate at the free edge — the nail separates in layers. Common in people who work with water frequently, use acetone nail products, or have thyroid disease. Easily distinguished from Beau’s lines by location (free edge splitting vs. proximal groove).
Diagnosis: How We Evaluate Horizontal Ridges in the Clinic
When a patient presents to Balance Foot & Ankle with horizontal nail ridges, our evaluation begins with a careful history. The most important question: “Did you have a significant illness, surgery, or health event 2-6 months ago?” When the answer is yes and the groove position matches the timing, we have our diagnosis. Most of these patients need nothing more than reassurance that the line will grow out over 6-12 months.
For multiple lines, bilateral lines without a clear precipitating event, or lines in combination with other nail changes, we examine: number and depth of lines, whether all nails are affected simultaneously (suggests systemic cause) or only one nail (suggests local cause), associated nail color changes (yellow, white, brown), nail texture (brittle, splitting, pitting), and surrounding skin changes (periungual erythema, swelling).
Laboratory evaluation may include: complete blood count (anemia, infection markers), metabolic panel (albumin, kidney function, glucose), thyroid function tests, zinc and iron studies, and inflammatory markers (ESR, CRP) if inflammatory disease is suspected. In patients with single-nail involvement and no systemic history, we consider local causes including past trauma or ill-fitting footwear causing matrix pressure.
⚠️ See a podiatrist or physician for horizontal nail ridges if you notice
- Multiple deep ridges appearing over weeks to months without a clear past illness to explain them
- Ridges affecting only one nail combined with nail discoloration, thickening, or separation from the nail bed
- Ridges accompanied by hair loss, fatigue, muscle weakness, or other systemic symptoms
- Very deep grooves that look like the nail might break at the groove
- Ridges in the context of known chronic disease (diabetes, thyroid disease, autoimmune conditions) that have been progressing
- New ridges appearing after starting a new medication — especially chemotherapy, retinoids, or antifungals
Treatment: Do Beau’s Lines Go Away?
For Beau’s lines caused by a single past event (illness, surgery, fever), the answer is yes — without any treatment. The groove grows forward at the toenail’s natural growth rate and is eventually trimmed off at the free edge. The entire process takes 6-12 months for a great toenail, less for smaller toes. There is nothing you can apply topically or take orally to speed this up. Biotin, nail hardeners, and other nail supplements do not affect Beau’s line resolution.
When Beau’s lines reflect an ongoing condition — an uncontrolled chronic disease, an active nutritional deficiency, or a medication effect — treatment is directed at the underlying cause. Correcting the deficiency or managing the disease will halt new line formation; existing lines will continue to grow out normally once the trigger is removed.
During the period while the line is growing out, the nail at the groove is structurally weaker than normal nail. You do not need to do anything specific, but avoid very aggressive trimming right at the groove and be cautious with the nail during that area’s growth. In rare cases where a groove is very deep, the nail can break at the groove; keeping nails trimmed at appropriate length (not too long) and wearing well-fitting footwear reduces this risk.
Key takeaway: Beau’s lines from a past single event: grow out on their own in 6-12 months, no treatment needed. Ongoing or recurrent Beau’s lines: identify and treat the underlying cause.
Frequently Asked Questions
Are horizontal ridges on toenails serious?
A single horizontal ridge appearing after a known illness, high fever, or surgery is not serious — it is a normal nail response to physiological stress that will grow out on its own. Multiple ridges without a clear cause, or ridges accompanied by other symptoms, are worth evaluating because they can indicate an underlying condition such as nutritional deficiency, thyroid disease, or circulatory problems.
What is the difference between Beau’s lines and vertical ridges?
Beau’s lines run side-to-side (transversely) across the nail and feel like grooves when you run your fingernail over them. Vertical ridges run lengthwise from base to tip of the nail and are almost always a normal part of aging. Vertical ridges are extremely common after 50 and rarely signify anything medically important. Horizontal ridges (Beau’s lines) are less common and more diagnostically significant.
Can COVID-19 cause horizontal ridges on toenails?
Yes. COVID-19 has been associated with Beau’s lines, typically appearing 1-3 months after the acute illness. The physiological stress of the infection temporarily suppresses the nail matrix, creating the characteristic grooves. These lines are benign and grow out normally over 6-12 months. This is one of the more common nail findings we have seen since 2020-2021 in our practice.
How long does it take for Beau’s lines to grow out?
Toenails grow approximately 1.5-2 mm per month. A Beau’s line near the nail base will take 6-12 months to reach the free edge and be trimmed away, depending on which toenail is affected (the great toenail takes longest). There is no treatment to speed this up. Once the underlying cause is resolved, no new lines form, and the existing groove grows out naturally.
Should I be worried about horizontal ridges after chemotherapy?
Horizontal ridges after chemotherapy are expected and benign. Many cytotoxic agents temporarily suppress the nail matrix, producing Beau’s lines that correspond to each treatment cycle. These lines grow out after treatment ends. If you notice nail changes during chemotherapy beyond simple ridges — such as nail lifting (onycholysis), color changes, or severe brittleness — mention them to your oncologist, as some nail changes during chemotherapy can signal treatment-related toxicity.
The Bottom Line
Horizontal ridges on toenails — Beau’s lines — are the nail’s way of recording a past physiological disruption. A single groove after a major illness or surgery is almost always benign and will grow out in 6-12 months without any intervention. Multiple lines without a clear precipitating event, or lines combined with other nail or systemic changes, are worth a medical evaluation to rule out ongoing nutritional deficiency, chronic disease, or medication effects.
The most important step is distinguishing horizontal ridges from vertical ridges — the far more common, essentially-always-benign age-related change that runs lengthwise along the nail. If your ridges run side-to-side and you had a significant illness 2-6 months ago, the mystery is almost certainly solved. If not, we are glad to evaluate.
Sources
1. Tosti A, Piraccini BM, Cameli N. Beau’s lines and onychomadesis following hand-foot-mouth disease: a case report. Arch Dermatol. 1999;135(2):212.
2. Tully AS, Trayes KP, Studdiford JS. Evaluation of nail abnormalities. Am Fam Physician. 2012;85(8):779-787.
3. Wollina U, Nenoff P, Haroske G, Haenssle HA. The Diagnosis and Treatment of Nail Disorders. Dtsch Arztebl Int. 2016;113(29-30):509-518.
4. Iorizzo M, Pazzaglia M, Piraccini BM, Tosti A. Brittle nails. J Cosmet Dermatol. 2004;3(3):138-144.
5. Starace M, Bergamin M, Piraccini BM. Nail changes in COVID-19 patients: a systematic review. Dermatol Ther. 2021;34(6):e15143.
Green nail discoloration has very different causes from horizontal ridges — a Pseudomonas infection or trauma-related issue. See our guide: Green Toenail Discoloration: A Related Nail Change.
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For a complete clinical overview: Toenail Problems Complete Guide — nail discoloration, ridges, fungus, and injury treated
PubMed: Beau Lines — Horizontal Nail Ridges Causes & Treatment
In-Office Treatment at Balance Foot & Ankle
If home care isn’t resolving your symptoms — or if you’re unsure of your diagnosis — a same-visit evaluation with Dr. Tom Biernacki, DPM gives you a clear diagnosis and a treatment plan the same day. We serve patients in Howell and Bloomfield Hills, MI. Book online →
Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon 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 reached over one million views.
A single horizontal dent across your big toenail usually traces back to one moment 4–6 months ago — an illness, a fever, or a medication you forgot you took. But one ridge pattern means stop reading and call a doctor today. Here is how to tell which is which, in plain English from a board-certified podiatrist.
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Specialist For This Condition
Dr. Daria Gutkin, DPM, AACFAS is the Balance Foot & Ankle podiatrist most patients ask for when horizontal ridges, dents, or systemic-related nail changes need careful evaluation. Cleveland Clinic-trained, bilingual (English / Russian), known as the gentlest hands in Michigan podiatry. Call (810) 206-1402 to request at the Howell or Bloomfield Hills office.
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.