Onychia is an infection or inflammation of the nail itself, causing swelling, pain, and visible changes to the nail plate. It can affect fingernails or toenails and is most commonly triggered by bacteria, fungi, or physical trauma to the nail. While it often resolves with basic care, untreated onychia can lead to pus buildup, nail damage, or even permanent changes to the way a nail grows.
Onychia vs. Paronychia
These two terms are easy to confuse because they affect the same area and share similar symptoms. The key difference is location. Onychia is an infection of the nail plate itself, while paronychia is an infection of the skin folds surrounding the nail. In practice, the two conditions often overlap: inflammation that starts in the tissue around the nail can spread into the nail, and vice versa.
Paronychia tends to show up first as redness, tenderness, and swelling along the edges of the nail. Onychia, by contrast, centers on the nail plate and the tissue directly beneath it. Both can produce pus-filled abscesses, nail hardening, deformation, and in severe cases, separation of the nail from the nail bed.
Common Causes
Onychia has both infectious and non-infectious triggers. Bacterial infections are the most frequent cause, often entering through small breaks in the skin near the nail. Biting your nails, picking at cuticles, aggressive manicures, or minor injuries like stubbing a toe can all create an opening for bacteria. Exposure to oral bacteria (from nail biting, for example) may introduce a wider range of organisms.
Fungal nail infections are another major cause, particularly for toenails. Fungal onychia (sometimes called onychomycosis) affects roughly 1 to 8% of the general population, but rates climb sharply in people with weakened immune systems. Among patients on kidney dialysis, fungal nail infections show up in 19 to 52% of cases. Diabetes, psoriasis, obesity, HIV, and older age all raise the risk. Men tend to be affected more often than women.
Less commonly, viral infections like herpes simplex can cause nail inflammation. Non-infectious causes include repeated chemical exposure (detergents, solvents), prolonged moisture, and skin conditions like eczema that weaken the nail’s natural defenses.
What It Looks and Feels Like
Early onychia typically presents as redness, warmth, and tenderness around the nail. The nail itself may look discolored, thickened, or slightly lifted from the nail bed. At this stage, there is usually no pus, just inflammation.
If the infection progresses, pus can collect beneath or around the nail, forming a visible abscess. The nail may become increasingly deformed, ridged, or brittle. In severe cases, the nail separates from the underlying skin entirely, a process that can be painful and alarming but is the body’s way of shedding a damaged nail. Chronic or recurring infections can eventually cause permanent changes to the nail’s shape and texture, a condition called nail dystrophy.
How Onychia Is Treated
Treatment depends on the stage and severity of the infection. In the early phase, when inflammation is present but no pus has formed, most cases can be managed without surgery. Warm soaks several times a day help reduce swelling and draw out infection. Keeping the affected hand or foot clean and dry between soaks is important, as moisture feeds many of the organisms involved.
When a bacterial infection is suspected, oral antibiotics are typically prescribed for 7 to 10 days. The choice of antibiotic depends on local resistance patterns, including how common drug-resistant bacteria like MRSA are in your area. For fungal infections, antifungal medications are used instead, and these often require a longer course of treatment because fungi grow slowly and are harder to eliminate from nail tissue.
If an abscess forms with visible pus beneath or around the nail, surgical drainage becomes necessary. This is a minor in-office procedure where a healthcare provider opens the abscess to let the infected fluid escape. In some cases, part or all of the nail needs to be removed to access and drain the infection underneath. At least one study has suggested that if drainage is thorough, antibiotics may not always be needed afterward, though most providers still prescribe them as a precaution.
Recovery and Nail Regrowth
Mild cases of onychia often improve within a week or two with proper care. More severe infections, especially those requiring drainage or nail removal, take longer. The soft tissue heals in a matter of weeks, but the nail itself is another story.
Fingernails take about 4 to 6 months to grow back fully. Toenails are significantly slower, requiring up to 18 months for complete regrowth. After trauma or medical removal, the timeline can stretch from 6 months to 2 years. The new nail may initially look slightly different in texture or color, but in most cases it eventually returns to normal, provided the nail matrix (the tissue that generates nail growth) was not permanently damaged by the infection.
Who Is Most at Risk
Certain groups are disproportionately affected. People with diabetes have reduced blood flow and immune function in their extremities, making nail infections both more likely and harder to clear. Kidney dialysis patients face some of the highest rates, with nearly half showing nail changes in one study of 151 patients. Obesity independently increases the risk by roughly threefold. Immunosuppressed individuals, including organ transplant recipients and those with HIV, are also more vulnerable.
Occupation matters too. People who frequently immerse their hands in water (dishwashers, bartenders, healthcare workers, cleaners) soften their nails and surrounding skin, creating easy entry points for bacteria and fungi. Nail salon workers and their clients face risk from improperly sterilized tools.
Preventing Nail Infections
The CDC recommends several straightforward habits. Clean nail grooming tools before each use, and in nail salons, insist that tools are sterilized between clients. Do not cut your cuticles, because they serve as a physical barrier that keeps bacteria and fungi from reaching the nail root. Never rip or bite a hangnail. Instead, clip it cleanly with sanitized trimmers.
Beyond tool hygiene, keep your nails trimmed and dry. Wear gloves when working with water, chemicals, or soil for extended periods. If you notice early signs of inflammation (redness, tenderness, slight swelling), start warm soaks right away rather than waiting for the infection to worsen. People with diabetes or compromised immune systems should pay extra attention to their nails and seek care promptly at the first sign of trouble, since what starts as minor inflammation can escalate quickly when the body’s defenses are impaired.