A burning sensation beneath a fingernail or toenail is often localized, intense, and immediately concerning. This specific type of pain, known as onychalgia, arises because the nail unit contains a dense network of nerves, making it highly sensitive to pressure, irritation, and inflammation. Understanding the source of this discomfort requires looking at causes ranging from simple mechanical injuries to complex medical conditions.
Immediate Physical Causes and Irritants
One of the most common causes of intense burning under the nail is a subungual hematoma, which is blood trapped beneath the nail plate following a crushing injury. The hard nail prevents the blood from escaping, causing a rapid buildup of pressure on the highly innervated nail bed beneath. This pressure on the nerve endings creates the severe, pulsatile pain.
Acute exposure to caustic substances can cause a chemical burn beneath the nail, leading to inflammation. Harsh cleaning agents, strong solvents, or chemicals in nail products can penetrate the nail plate, causing tissue damage and an inflammatory reaction. Additionally, a microscopic foreign body, such as a tiny splinter, can become lodged in the nail bed, triggering nerve irritation perceived as a sharp, localized burn.
Pathogens and Nail Bed Infections
Acute paronychia is a bacterial infection of the tissue around the nail fold, typically causing rapid onset of symptoms. Bacteria, most commonly Staphylococcus aureus, enter through a minor break in the skin, leading to warmth, redness, and throbbing pain as pus accumulates. This accumulation increases pressure on the nerve-rich nail bed.
Chronic paronychia is a more gradual process, often starting as an inflammatory skin reaction that allows secondary colonization by organisms like the yeast Candida albicans. This condition is common in people whose hands are frequently wet, as constant moisture breaks down the natural seal between the nail fold and the nail plate. The resulting chronic inflammation and swelling around the cuticle can cause persistent discomfort and a secondary burning sensation.
Fungal infections of the nail plate, known as onychomycosis, usually begin with discoloration and thickening, but they can also cause pain. As the fungus grows, it causes a buildup of debris underneath the nail plate, called subungual hyperkeratosis. This debris elevates the nail, placing pressure on the nail bed and leading to pain or a mild burning feeling, especially when the nail is pressed or when wearing tight shoes.
Systemic and Rare Conditions
A persistent burning sensation can signal a deeper medical issue, such as a Glomus tumor. This rare, benign growth originates from the glomus body, a specialized structure involved in temperature regulation. These small tumors occur most frequently under the nail bed and are known for causing excruciating, episodic burning pain, characteristically triggered or intensified by cold temperatures.
A burning feeling may also result from conditions affecting the nerves, such as peripheral neuropathy or nerve entrapment in the finger. When a nerve that supplies the digit is compressed, such as in carpal tunnel syndrome, it can cause abnormal sensations like tingling, numbness, or a chronic burning feeling that radiates into the fingertip. Inflammatory skin disorders like nail psoriasis can also affect the nail bed, causing severe inflammation, thickening, and painful separation of the nail plate from the bed.
Seeking Professional Diagnosis
A mild, temporary burning sensation following an obvious injury may resolve with basic care, but certain signs require immediate medical attention. Consult a healthcare provider if the pain is persistent, worsening, or severe enough to disrupt sleep. Important red flags include signs of spreading infection, such as fever, red streaks extending from the nail, or the presence of thick pus. A professional assessment may involve imaging or lab tests to differentiate between trauma, infection, nerve issues, or a tumor, ensuring the correct treatment.