Allodynia is the experience of pain from a non-painful stimulation of the skin, such as light touch. Learn how allodynia and migraine are related and what you can do to treat allodynia symptoms during a migraine attack.
Allodynia is a type of nerve pain that causes a heightened sensitivity to touch and other contact to the skin. It results from a stimulus that is not normally painful (the word allodynia itself means “other pain”). Anyone who has ever had a bad sunburn has an idea of how painful even light touch can be when the skin is highly sensitized—for example, even putting on a shirt or taking a shower can be very painful.
Allodynia can be one of the more surprising symptoms of a migraine attack. In fact, up to 80% of people with migraine experience at least one allodynia symptom during an attack. Learn what causes allodynia and why it is so often associated with migraine and other chronic pain conditions.
Types and Symptoms of Allodynia
Because allodynia can occur across the entire surface of the skin, people may experience a range of different symptoms, from pain or sensitivity to touch to a heightened sensitivity to temperature changes. There are three types of allodynia:
- Tactile (“static”) allodynia refers to experiencing pain when an object makes contact with the skin, such as when resting one’s head on a pillow or putting on clothing or jewelry.
- Mechanical (“dynamic”) allodynia refers to pain from an object moving across the skin, like when lightly brushing one’s hair or shaving one’s face.
- Thermal allodynia refers to pain due to exposure to either warm or cold temperatures.
Allodynia is not referred pain, although it can occur outside of the area that is directly stimulated. It is also not hyperalgesia—a painful stimulus typically caused by nerve damage.
The severity of allodynia varies widely from person to person. Allodynia is rated by both the frequency with which each symptom occurs and by how many different symptoms are present. Primary headache-related allodynia occurs more often in people with migraine than in those with tension-type headache.
What causes allodynia?
There are many conditions that can cause allodynia, including migraine, diabetes, chronic pain conditions and others.
Among people with migraine, allodynia is more common in people living with chronic migraine, migraine with aura, and those who typically experience severe, disabling headache attacks. Allodynia is associated with more disability when objectively measured by MIDAS (Migraine Disability Assessment Scale). The more years a person has lived with migraine, the more likely they are to experience allodynia.
Women experience migraine and allodynia more often than men. Female reproductive hormones lower the intensity of the pain stimulus needed to produce pain. This process lowers the pain threshold and likely involves mechanisms that produce symptoms such as allodynia.
Research shows that being overweight or obese and smoking predispose a person to allodynia. Obesity is more common in people with chronic migraine, and this may account for the increased rates of allodynia. Like female hormones, smoking also reduces the pain threshold. Additionally, a stressful childhood marked by emotional abuse increases the frequency of headache and allodynia as an adult.
Allodynia and Migraine: Central Sensitization
All of these associations suggest allodynia is a risk factor for worsening headache progression. They also raise questions when it comes to migraine treatment: Does the presence of allodynia have an effect on migraine treatment? Should we use allodynia as a marker for beginning prevention therapy?
Research suggests that allodynia in migraine results from a process within the brain and spinal cord, which make up the central nervous system. Scientists call this process “central sensitization.”
The process begins when sensory pain nerves, known as nociceptors, react to a sensory signal or stimulus. In the case of migraine, inflammation surrounding the blood vessels on the surface of the brain play a role. The nerve endings around the blood vessels send signals along the nerves to the central nervous system. This can result in the throbbing head pain many people experience during a migraine attack. Acute pain treatment stops the signals coming in from the peripheral nerves. However, if these signals are not stopped, the nerves in the spinal cord and brainstem can become overly sensitized or hyperexcitable. This is central sensitization.
As a consequence, even normal sensory signals, such as touch on the scalp and face, produce abnormal pain responses. The pain feels as if it is coming from the skin, but is actually the result of a mixed-up processing of sensory signals within the central nervous system. Frequent, severe attacks of migraine—particularly migraine with aura—over a long period of time can lead to an increased tendency for central sensitization. Allodynia is a manifestation of this central sensitization.
Can allodynia be treated with migraine medications?
For most people, allodynia resolves when the pain from a migraine attack resolves. In some cases, allodynia may persist after the headache phase subsides. If headaches progress into a chronic or daily occurrence, allodynia may become a daily, continuous condition.
Triptans, a type of acute migraine medication, are often less effective once allodynia is present as a symptom during a migraine attack. For this reason, it is important to treat attacks early before allodynia appears.
If possible, use acute treatment before the pain begins to take on a throbbing quality. Throbbing is a sign of peripheral sensitization, a process that precedes central sensitization. Unlike central sensitization, peripheral sensitization is easy to stop with triptans and other effective migraine therapies.
Studies show that some medications work when allodynia is present. Ketorolac, a nonsteroidal anti-inflammatory drug, and dihydroergotamine work when injected with allodynia present.
Allodynia and Chronic Pain Conditions
People with migraine often experience other chronic pain conditions, such as fibromyalgia, irritable bowel syndrome, and chronic fatigue syndrome.
Fibromyalgia is characterized by tender painful muscles above and below the waist. Like chronic migraine and chronic tension-type headache, scientists believe central sensitization also causes these chronic conditions. These disorders make up a group known as the central sensitivity syndromes. People with migraine who experience allodynia are more likely to also have one or more of these other pain conditions.
Even when these conditions occur without migraine, they may co-occur with allodynia. Furthermore, the severity of allodynia in migraine correlates with the number of different pain conditions a person has, offering further evidence that a common, underlying cause may link these conditions together. It may be that if central sensitization develops with one condition, this predisposes a person to developing additional pain conditions. Depression and anxiety are also common in people with allodynia-associated migraine and the other pain syndromes, but the cause for this link remains uncertain.
Allodynia arises from the brain, and stopping pain signals early can ward off symptoms. Preventing pain from recurring frequently can reduce the likelihood of chronic allodynia. If allodynia occurs frequently, talk to your doctor about preventive treatments and other ways to reduce the risk of it becoming a chronic condition.
The American Migraine Foundation is committed to improving the lives of those living with this debilitating disease. For more of the latest news and information on migraine, visit the AMF Resource Library. For help finding a healthcare provider, check out our Find a Doctor tool. Together, we are as relentless as migraine.
Gretchen E. Tietjen, MD, Professor and Chairman of Neurology, University of Toledo, Toledo OH.