Brittle toenails can be more than a cosmetic concern, and the pattern of cracking, splitting, or thinning often points to an underlying cause.
Understanding what causes brittle toenails can help you narrow down whether the issue is due to a fungal infection, repeated trauma, aging, or a health condition that needs treatment.
What causes brittle toenails?
Brittle toenails usually develop when the nail plate loses moisture, becomes structurally weak, or grows in an environment that repeatedly damages it.
In some cases, the problem is limited to the nail itself; in others, it reflects changes in circulation, hormones, nutrition, or skin disease.
The most common causes include fungal infection, frequent exposure to water or chemicals, tight footwear, and age-related nail changes.
Less commonly, brittle toenails are linked to thyroid disease, psoriasis, iron deficiency, and certain medications.
Fungal infections
Onychomycosis, the medical term for fungal nail infection, is one of the leading causes of toenail brittleness.
The nail may become thick, discolored, crumbly, and difficult to trim as the infection weakens its structure.
Fungal infections are more likely to affect toenails than fingernails because shoes create a warm, moist environment where fungi such as dermatophytes can thrive.
Risk increases in people who frequent locker rooms, public pools, or shared showers.
Repeated trauma to the toenails
Constant pressure or impact can make toenails brittle over time.
This is common in runners, dancers, hikers, and anyone who wears shoes that rub the toes or crowd the forefoot.
Even minor repeated trauma can cause microdamage in the nail plate and nail bed.
Over time, this may lead to splitting, peeling, ridging, or partial lifting of the nail from the skin underneath.
- Tight toe boxes that compress the nails
- Downhill running or repetitive stopping and starting
- Stubbing the toes or dropping objects on the feet
- Improper nail trimming that leaves edges vulnerable
Moisture loss and frequent wet-dry cycles
Toenails need a balance of hydration to remain flexible.
Excessive dryness can make them more likely to crack, while repeated soaking followed by drying can weaken the nail plate.
People who swim often, work in wet environments, or wash their feet excessively may notice that nails become more fragile.
Harsh soaps, acetone-based removers, and drying foot products can worsen the problem.
Aging and slower nail growth
Age is a common reason toenails become brittle.
As people get older, nails often grow more slowly, lose some of their natural moisture, and become more prone to splitting and ridging.
Slower growth also means damage takes longer to grow out.
This can make a nail injury or fungal infection seem more persistent, even when the trigger was minor.
Nutritional deficiencies
Dietary issues can contribute to brittle toenails, especially when there is inadequate intake or absorption of key nutrients needed for healthy keratin production.
Iron deficiency is one of the most discussed associations, though protein, zinc, biotin, and other nutrients also matter.
Brittle nails alone do not prove a deficiency, but they may appear alongside fatigue, hair shedding, pale skin, or other signs of poor nutrition.
- Iron deficiency
- Low protein intake
- Zinc deficiency
- Insufficient biotin or B vitamins
Thyroid disorders
Both hypothyroidism and hyperthyroidism can affect nail growth and texture.
In hypothyroidism, nails may become dry, slow-growing, and brittle, while hyperthyroidism can sometimes cause thinning or lifting of the nail plate.
If brittle toenails are paired with weight changes, temperature intolerance, fatigue, or hair and skin changes, a thyroid issue may deserve evaluation.
Psoriasis and other skin conditions
Psoriasis can affect the nail matrix and nail bed, leading to thickening, pitting, discoloration, and brittleness.
Eczema and lichen planus may also alter nail integrity, though toenail involvement is less common than in the fingernails.
In these cases, the nails are usually only one part of a broader skin pattern that may include scaling, itching, inflamed patches, or changes elsewhere on the body.
Circulation problems and systemic disease
Poor blood flow can reduce the delivery of oxygen and nutrients needed for healthy nail growth.
Peripheral artery disease, diabetes, and other circulatory disorders may contribute to nail fragility, slower healing, and increased risk of infection.
Systemic illness can also alter the shape and growth rate of toenails.
When brittle nails occur with numbness, leg pain, foot ulcers, or slow-healing skin breaks, medical assessment becomes more important.
Medications and chemical exposure
Some medications and chemical exposures can dry or weaken nails.
Retinoids, chemotherapy drugs, and certain prescription treatments may influence nail quality, while frequent contact with detergents, solvents, and aggressive cleansers can strip protective oils from the nail unit.
Occupational exposure matters as well.
People who work with cleaning agents, industrial chemicals, or wet materials often have more nail dehydration and surface damage.
How brittle toenails are evaluated
Evaluation usually starts with a history of symptoms, footwear habits, grooming practices, and any skin, hair, or systemic changes.
A clinician may examine the nails for thickening, separation, color changes, or signs of fungal infection.
Depending on the appearance and symptoms, testing may include a nail scraping for fungal culture or microscopy, bloodwork for iron or thyroid issues, or a broader skin examination for psoriasis or dermatitis.
When to seek medical care
You should consider medical evaluation if the brittle toenails are painful, rapidly worsening, infected, or affecting several nails at once.
Care is also appropriate if the nails are lifting, changing color, or accompanied by swelling, redness, or drainage.
Prompt attention is especially important for people with diabetes, poor circulation, immune suppression, or recurrent foot infections because small nail problems can become larger foot problems.
Practical ways to reduce nail brittleness
Once you understand what causes brittle toenails, prevention becomes more targeted.
The right approach depends on the trigger, but several habits can support healthier nails in many cases.
- Wear properly fitted shoes with enough toe room
- Keep toenails trimmed straight across and not too short
- Dry feet thoroughly after bathing or swimming
- Use moisturizer on the feet and nails if dryness is an issue
- Limit exposure to harsh soaps, acetone, and chemicals
- Treat fungal infections early rather than waiting for spread
- Maintain a balanced diet with adequate protein and iron
If you are unsure what causes brittle toenails in your case, the most useful clue is often the pattern: one nail versus many, thickened versus thin, painful versus painless, and whether there are skin or systemic symptoms alongside the nail change.