Nail Pitting and Onycholysis: What Your Nails Are Signalling

Nails are dense, slow-growing structures, and that slowness is exactly what makes them useful diagnostically. A change that appears at the tip today may reflect something that began at the matrix, the growth zone tucked under the base of the nail, weeks or months ago. Nail pitting and onycholysis are two of the more common nail findings a dermatologist will look for, and both carry a list of possible causes long enough that self-diagnosis reliably misses the point.

Nail pitting presents as small depressions on the nail surface, shallow, irregular craters that can appear in clusters, rows, or scattered randomly across one or several nails. The pits form when clusters of parakeratotic cells (cells that retain their nuclei instead of shedding cleanly) are incorporated into the nail plate as it grows and then fall away, leaving a gap behind. The result looks like someone pressed the tip of a pin into the plate at irregular intervals.

The number of pits and their arrangement carry some diagnostic weight. Psoriasis is the most common driver, and the pitting it produces tends to be irregular and numerous, sometimes described as a geographic pattern. Alopecia areata, an autoimmune condition affecting hair follicles, more often produces pits in regular geometric rows, sometimes called a grid pattern, because the matrix inflammation is more uniform. Eczema and atopic dermatitis can also cause pitting, though typically less pronounced. Reactive arthritis and other inflammatory arthropathies are associated with nail changes including pitting, particularly when multiple nails are involved.

Pitting alone does not confirm any of these conditions. A dermatologist will look at the full picture: the pattern of pits, whether other nail changes are present, and what is happening elsewhere on the skin and in the joints.

Onycholysis is the separation of the nail plate from the nail bed, beginning at the free edge and extending proximally toward the base. The separated area appears white or yellowish because air replaces the translucent contact between plate and bed. In some cases the detached zone has a well-defined border; in others it is irregular.

The causes divide broadly into local and systemic. Local causes include repeated trauma, nails that are too long, caught repeatedly on fabric, or subjected to aggressive manicure work, and contact with irritants or allergens, including some nail hardeners and gel adhesives. Fungal infection, specifically onychomycosis, is one of the most common local causes and produces onycholysis that typically starts at the distal edge and may be accompanied by thickening and discolouration of the plate.

Systemic causes are where the clinical picture becomes more complex. Psoriasis causes onycholysis through a different mechanism than fungal infection, the nail bed itself becomes inflamed and the plate loses its attachment. Thyroid dysfunction, both hypothyroidism and hyperthyroidism, is a recognised systemic cause. Iron deficiency anaemia, pregnancy, and certain medications, including tetracyclines, which can cause photo-onycholysis when the nail is exposed to sunlight, are all documented associations. The separation seen in psoriatic onycholysis often has a salmon-pink or oil-drop discolouration at its border, a finding that helps distinguish it from fungal causes, though laboratory confirmation is still required.

Treating onycholysis as a fungal infection when it is driven by psoriasis, or vice versa, delays the correct management and can worsen the underlying condition. Antifungal treatment does nothing for psoriatic nail disease. Conversely, immunosuppressive therapy for psoriasis in the presence of active fungal infection creates a different problem entirely.

This is why a nail scraping or clipping for microscopy and culture is often the first step when onycholysis is present, even when psoriasis is already diagnosed. Co-existing conditions are common. The same logic applies to pitting: finding psoriatic pitting does not rule out a concurrent fungal infection in the same nail.

Self-treating nail changes, particularly with over-the-counter antifungal products, without a confirmed diagnosis is one of the more common reasons nail conditions are still active months after someone first noticed them. Incorrectly identifying the cause and treating for it does not just fail to help; in some cases it obscures the clinical picture when the person eventually sees a dermatologist.

A clinical assessment of nail changes goes beyond the nail itself. A dermatologist will examine the skin of the scalp, elbows, knees, and umbilicus for psoriatic plaques; look for signs of scalp or body hair loss that might suggest alopecia areata; ask about joint pain or swelling; and review any medications, including supplements, that could be driving the change.

Dermoscopy, a magnified examination of the nail plate and periungual skin, has become a standard part of the assessment. It allows closer inspection of the oil-drop sign in psoriasis, the pattern of pitting, and the characteristics of the onycholysis border. In some cases, a nail biopsy is required to reach a definitive diagnosis, though this is reserved for presentations that do not resolve with initial treatment or where the diagnosis remains uncertain after other investigations.

Both pitting and onycholysis require clinical diagnosis. Attempting to identify the underlying condition from photographs or symptom lists is unreliable, and incorrectly self-treating certain causes, particularly fungal versus inflammatory, can make the nail worse and delay appropriate care. If nail changes have persisted for more than a few weeks, or if multiple nails are involved, a dermatologist is the right starting point.

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