Allodynia is a type of neuropathic pain. Someone who has allodynia feels unexpected pain from non-painful stimuli, like from a light touch or when brushing their hair.

Allodynia is defined as “pain due to a stimulus that does not normally provoke pain.” Individuals with allodynia feel pain when something is ordinarily painless.

Some people feel extreme pain from something minor, such as a paper cut. Feeling increased pain or being hypersensitive to mild pain is called hyperalgesia.

Allodynia is different from hyperalgesia, although a person may have both. In allodynia, a person can feel pain with a stimulus that does not usually cause pain, such as the brush of a feather.

Experts do not know precisely why allodynia happens, but it is most likely a symptom of a nerve condition. One theory is that certain nerve fibers are crossed, leading to unusual reactions.

There may be links with other conditions, such as fibromyalgia, trigeminal neuralgia, diabetic neuropathic pain, and migraine.

Here, learn about the symptoms of allodynia, why it happens, and how to manage it.

A person's back and loose hair, which may trigger allodyniaShare on Pinterest
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The main symptom of allodynia is pain.

Pain is a protective mechanism that tells a person to stop doing something harmful. For instance, a pain response causes a person to pull their hand away from a hot stove, preventing a severe burn.

For people with allodynia, pain occurs even though nothing harmful is causing it. A light touch, such as washing the face, a few hairs touching the skin, or a breath of air may be painful.

According to the American Migraine Foundation, allodynia can feel like having sunburn all over the body.

Symptoms can range from mild to severe, and the sensations can also vary. Some people may feel a burning sensation, while others feel an ache or squeezing pain.

Allodynia can limit a person’s activities and affect their quality of life. Symptoms may also worsen over time.

Ways of describing allodynia include:

  • Thermal allodynia: Pain occurs when there is a mild change of temperature on the skin. For example, a few drops of cold water on the skin may be painful.
  • Dynamic or mechanical allodynia: Movement — such as bedsheets pulled across the skin — may be painful.
  • Static or tactile allodynia: A light touch or pressure on the skin, such as a light tap on the shoulder, causes pain.

People may also describe it according to the part of the body where it occurs. For instance, cutaneous allodynia affects the skin.

Some people may only have one type of allodynia. Others may have several types.

The pain is related to nerves inside the body. It can affect different parts of the body depending on the type of allodynia and the underlying cause.

Experts do not know precisely why allodynia happens, but it is a type of neuropathic pain that involves sensitization.

Sensitization occurs when a nerve is damaged, and the nerves become hypersensitive. This can cause the nerve endings to release higher quantities of neurotransmitters, leading to nerve inflammation. Allodynia or hyperalgesia can result.

Allodynia may happen when nerves carry pain messages incorrectly, possibly due to a crossover of nerve fibers. There may be increased responsiveness or a malfunction in a type of nerve ending known as nociceptors.

Nerve damage can result from a health condition or injury or for no apparent reason. It can occur in the peripheral nervous system and lead to sensitization in the central nervous system.

It can also change over time or with different emotional states.

Having one of the following medical conditions may also increase a person’s risk of developing allodynia.

Migraine

Migraine can cause debilitating headache and other symptoms, such as sensitivity to sound and light. At least 65% of people with migraine experience symptoms of allodynia during an attack, and 20% have severe cutaneous allodynia. The American Migraine Foundation points out that allodynia can occur with a migraine attack but may or may not disappear after.

Postherpetic neuralgia

Postherpetic neuralgia (PHN) is a complication of shingles, which comes from the same virus as chicken pox. Shingles can damage nerve fibers and lead to persistent nerve pain.

The authors of one study say that “most” people with PHN experience tactile allodynia.

Fibromyalgia

Fibromyalgia causes widespread pain in the body. There may be a link between allodynia and fibromyalgia.

Diabetic neuropathy

Diabetes can cause nerve damage and increase the risk of nerve pain, including allodynia.

Nerve growth factor (NGF) is essential to the nervous system, and some experts have suggested that diabetes can lower NGF levels. A 2017 rodent study linked low levels of NGF with both hyperalgesia and allodynia.

Complex regional pain syndrome

Complex regional pain syndrome (CRPS) involves long lasting, excessive pain in a limb, typically following an injury. A person with CRPS may notice allodynia after using the limb or after light physical contact.

Having chemotherapy, surgery, or a traumatic injury can also increase the risk of having allodynia.

No single test can diagnose allodynia.

Instead, a doctor will:

  • perform a physical exam
  • take a medical history
  • review a person’s symptoms

They may ask questions such as:

  • When did the symptoms start?
  • Are they getting worse?
  • Do they come and go?
  • How would you describe this pain?
  • Have you taken any medications for it?
  • What makes it better, and what makes it worse?
  • Do you feel the pain with touch, heat, movement, or something else?

During a physical examination, the doctor may:

  • deliver a light touch to the area
  • look for skin changes and other symptoms
  • use the back of a cold device, such as a spoon, to assess the reaction to temperature
  • test for strength and reflexes

As well as the affected area, the doctor will assess other areas and both sides of the body for comparison. They may also do tests to rule out other possible conditions before diagnosing allodynia.

Anyone experiencing unexplained or unexpected pain should seek medical advice.

Complementary and lifestyle approaches may help treat allodynia. The precise approach will depend on the cause of allodynia, the individual, and how symptoms affect them.

Lifestyle choices that may help include:

  • light exercise
  • following a varied diet
  • getting enough sleep
  • quitting smoking, as research shows smokers are more likely to experience chronic pain than nonsmokers

Lifestyle will not cure allodynia but can enhance people’s overall mental and physical health. This may make allodynia easier to live with.

People can also:

  • identify pain triggers and take measures to avoid them, where possible
  • choose fabrics, hair brushes, and other items that are less likely to cause pain
  • find ways to manage stress, as stress can worsen the symptoms of pain

People have tried cupping and acupuncture, but there is not enough research to confirm they will help. Since they involve touch, they may not be suitable for everyone with allodynia.

There is no cure for allodynia, but some treatments can reduce pain.

Here are some options:

  • pregabalin tablets
  • anticonvulsant tablets, including gabapentin
  • anti-depressants can help some people
  • topical pain medications containing lidocaine, a local anesthetic
  • topical creams containing menthol or capsaicin, although these may trigger thermal allodynia
  • other topical treatments containing gabapentin, ketamine, salicylates, and other ingredients

A doctor may also recommend:

Treating an underlying condition that is causing allodynia may also help. For example, taking medication to prevent migraine can reduce the risk of allodynia symptoms. Managing blood sugar levels can reduce the risk of diabetic neuropathy.

Allodynia is not life threatening, but it can make daily life challenging. It can also lead to anxiety and other mental health conditions.

The outlook for people with allodynia varies depending on the severity of the symptoms and any underlying conditions, such as diabetes or migraine.

Here are the answers to some questions people often ask about allodynia.

What is the difference between allodynia and hyperalgesia?

Hyperalgesia and allodynia are both types of hyperesthesia, where problems with the nervous system cause increased sensitivity to stimulation. Hyperalgesia is when people feel excessive pain from a minor injury or pain stimulus. In allodynia, the pain has no apparent cause, or a very gentle touch may trigger it. Some people have both allodynia and hyperalgesia.

What triggers allodynia?

People with shingles, diabetic neuropathy, fibromyalgia, and migraine often experience allodynia, but it can also occur after an injury or surgery.

Can allodynia go away without treatment?

Treatment for an underlying condition can cause symptoms to improve or disappear. In some cases, however, a person has allodynia alone, without an underlying condition. In this case, it can worsen over time, although treatment can help manage the symptoms.

People with allodynia experience pain that seems unrelated to the cause, or stimulus. It appears to result from a problem with the nervous system.

It can happen for various reasons, including an injury, surgery, migraine, fibromyalgia, or as a result of nerve damage due to diabetes.

Various oral and topical pain medications can help manage it. some non-drug and lifestyle measures may also help.