A sunburn is an acute inflammatory reaction in the skin caused by overexposure to ultraviolet (UV) radiation. The intense pain is a direct result of this inflammation acting on the peripheral nervous system. While a typical first-degree sunburn does not cause lasting nerve damage, it triggers significant, temporary nerve irritation known as hyperalgesia. Sustained nerve damage, or neuropathy, is generally only a concern in cases of severe, deep second- or third-degree burns that involve thermal destruction of tissue.
The Biological Connection Between UV Exposure and Pain
The intense pain begins when UV light damages epidermal cells, specifically keratinocytes. This injury causes keratinocytes to release chemical mediators, which are signaling molecules that initiate the inflammatory response. These mediators, including endothelin-1 and various cytokines, diffuse into the dermis, the layer beneath the epidermis.
The dermis is supplied with fine sensory nerve endings, including C-fibers and A-delta fibers, which transmit pain and temperature signals. When inflammatory chemicals reach these nerve endings, they effectively lower the nerves’ activation threshold. This process, known as peripheral sensitization, makes the nerves hypersensitive to stimuli, resulting in the characteristic tenderness and pain.
This temporary functional change in the nerve fibers is why even a light touch can feel painful on sunburnt skin. The heightened sensitivity is designed to protect the injured area and usually peaks between six and 48 hours after the initial sun exposure. The sensitivity resolves as the inflammation subsides and the skin begins to heal.
Identifying Signs of Sunburn-Related Nerve Irritation
The temporary nerve irritation manifests as distinct sensory symptoms beyond simple redness and heat. Primary among these is hyperalgesia, an exaggerated response to a painful stimulus. For instance, pressing lightly on the affected skin may cause pain far greater than normal.
Sunburn can also cause allodynia, a phenomenon where a normally non-painful stimulus, such as the gentle brush of clothing, triggers a painful sensation. This results from sensitized nerve fibers misinterpreting non-painful signals as pain-related information. The feeling can be described as a burning or stinging discomfort.
Some people also experience paresthesia, which includes transient feelings of tingling or “pins and needles.” In cases of severe inflammation, the swelling can temporarily compress superficial sensory nerves, leading to localized numbness. These signs are generally temporary and begin to fade as the skin’s inflammatory phase ends.
When Temporary Nerve Damage Becomes Serious
While most sunburns only cause temporary nerve irritation, lasting nerve damage, or peripheral neuropathy, is a risk with deeper burns. First-degree sunburns are limited to the epidermis. Deep second-degree burns damage the underlying dermis, and third-degree burns destroy the full thickness of the skin and sometimes the tissue beneath it. The nerve bundles that provide sensation are located in the dermis and deeper layers, making them vulnerable to destruction in these more severe injuries.
A primary sign of severe nerve destruction is a complete or significant loss of sensation in the burn area. In a third-degree burn, the area may feel numb because the nerve endings have been thermally destroyed. Damage can lead to persistent numbness, chronic neuropathic pain, and even motor weakness if deeper motor nerves are affected.
Persistent numbness that lasts more than 48 hours should be evaluated by a healthcare professional. Medical attention is also necessary if the burn is accompanied by signs of infection or if the affected limb experiences any accompanying motor issues, like an inability to move fingers or toes. These symptoms indicate severity beyond a typical sunburn and may require specialized burn care.