Wavy nails are usually caused by one of two things: normal aging or a temporary disruption to nail growth. The direction of the waves matters. Vertical lines running from your cuticle to the tip are almost always harmless. Horizontal dents or ridges running side to side can signal that something interrupted your nail’s growth cycle, from a high fever to a nutritional gap.
Vertical vs. Horizontal: Direction Tells the Story
Your nails grow from a cluster of cells called the nail matrix, tucked just beneath your cuticle. When that matrix produces nail cells evenly, the surface comes out smooth. When something disrupts the process, ridges form. The direction of those ridges points to very different causes.
Vertical ridges run lengthwise, from cuticle to tip. They tend to appear gradually and affect multiple nails at once. Horizontal ridges, called Beau’s lines, run across the nail like grooves or dents. They typically show up weeks after a specific event, like an illness or injury, and grow forward with the nail over time.
Why Vertical Ridges Are Usually Normal
Vertical ridges are the most common type of nail waviness, and aging is the top cause. As you get older, the cells in your nail matrix don’t turn over as evenly. The result is fine lines or raised ridges along the length of the nail. Reduced blood circulation to the fingertips and cumulative UV exposure may also play a role, though researchers haven’t pinned down the exact mechanism. Most people notice these ridges becoming more prominent in their 30s or 40s, and they tend to deepen with each decade.
A few health conditions can make vertical ridges worse or cause them earlier than expected:
- Iron deficiency. Low iron can produce vertical ridges and, in more severe cases, nails that curve inward like a spoon.
- Thyroid problems. Hypothyroidism often causes thick, brittle nails with noticeable vertical lines.
- Dry skin or eczema. Chronic skin dryness, especially around the nail bed, can translate into ridged nail surfaces.
If your vertical ridges are subtle, symmetrical across most of your nails, and aren’t accompanied by color changes or pain, they’re almost certainly a cosmetic issue rather than a medical one.
What Horizontal Ridges (Beau’s Lines) Mean
Horizontal dents are more worth paying attention to. They form when nail growth temporarily stalls or slows dramatically, leaving a visible groove in the nail plate. Because fingernails grow at roughly 3 mm per month, you can often estimate when the disruption happened by measuring how far the ridge is from your cuticle. A groove sitting 6 mm from the base likely formed about two months ago.
Common triggers for Beau’s lines include:
- High fevers and severe illness. COVID-19, pneumonia, and measles have all been linked to Beau’s lines appearing weeks after recovery. Several reports documented nail changes specifically after severe COVID infections.
- Chemotherapy. Cancer treatment frequently interrupts the rapidly dividing cells in the nail matrix.
- Zinc deficiency. Low zinc can cause Beau’s lines along with white spots on the nails.
- Severe malnutrition. When the body lacks protein or calories, nail growth is one of the first things it deprioritizes.
- Peripheral vascular disease. Poor blood flow to the hands and feet can starve the nail matrix of nutrients.
- Direct injury. Slamming your finger in a door or dropping something heavy on your toe can produce a single horizontal groove on that nail.
If Beau’s lines appear on just one or two nails, local trauma is the likely culprit. If they show up across many nails at the same position, a systemic event like illness or medication is more probable.
Nail Pitting and Rough Texture
Some people describe their nails as wavy when the surface is actually pitted or rough rather than ridged. Small dents or divots scattered across the nail are a hallmark of psoriasis, which affects the nail matrix in up to half of people with the skin condition. The pits tend to be relatively uniform and may appear alongside thickened or discolored nails.
Eczema and dermatitis can cause a coarser, more irregular form of pitting that looks different from psoriasis. The pits are less uniform and the nail surface may feel bumpy rather than dotted. A related condition called trachyonychia produces nails with a rough, sandpaper-like texture and excessive longitudinal ridging. It’s most common in children, where it sometimes affects all twenty nails. In adults, it’s often linked to alopecia areata (an autoimmune condition that causes patchy hair loss) or lichen planus.
Damage From Manicures and Habits
The nail matrix sits right beneath the cuticle, which makes it vulnerable to everyday habits. Aggressive cuticle pushing during manicures, long-term use of acrylic or gel nails, and even habitual nail biting can injure the matrix and produce ridges or waves. Scar tissue that forms in or beneath the matrix changes the shape of the nail as it grows out, creating a permanent longitudinal ridge in some cases.
The good news is that damage from habits is often reversible. Once you stop the behavior, whether that’s overzealous cuticle trimming, nail biting, or prying things open with your nails, the matrix can heal and the nail shape typically returns to normal as new growth replaces the damaged section.
How Long Ridges Take to Grow Out
Fingernails grow at an average rate of about 0.1 mm per day, or roughly 3 mm per month. A full fingernail takes four to six months to grow from cuticle to tip. That means a horizontal groove from an illness two months ago is still going to be visible for several more months as it slowly migrates toward the free edge. Toenails grow even slower and can take 12 to 18 months to fully replace.
If the underlying cause was a one-time event like a fever or injury, the ridge will eventually grow out completely. If the cause is ongoing, like an untreated thyroid condition or chronic eczema, new ridges will keep forming until the root issue is addressed.
Do Biotin Supplements Help?
Biotin is heavily marketed for nail health, but the evidence is limited. A review of published cases found that every person who improved with biotin supplementation had an underlying condition causing poor nail growth, such as brittle nail syndrome. Those individuals saw results at doses of 2,500 to 5,000 micrograms per day, typically within two to six months. However, no randomized controlled trials have shown that biotin improves nail texture in healthy people. If your ridges are from normal aging or a past illness, biotin is unlikely to make a difference.
Addressing actual deficiencies is more productive. If you suspect low iron or zinc, a blood test can confirm it, and correcting the deficiency through diet or supplements will often improve nail quality as new growth comes in.
Signs That Warrant a Closer Look
Most nail ridges are benign, but certain changes alongside waviness suggest something worth investigating. Color changes in the nail plate, particularly dark streaks, new yellowing, or a blue tint, deserve attention. Horizontal ridges appearing across multiple nails without an obvious recent illness could point to a vascular or metabolic issue. Nails that become extremely thick, crumbly, or that separate from the nail bed are also worth bringing up with a healthcare provider. Vertical ridges alone, without these additional changes, are rarely a cause for concern.