A migraine is a complex neurological event that unfolds in up to four distinct phases, each with its own set of symptoms. It goes far beyond a bad headache. The full experience can stretch from a few hours to several days, involving changes in mood, vision, pain processing, and cognitive function. The World Health Organization ranks migraine as the third highest cause of disability worldwide among all neurological conditions.
It Starts in the Brain, Not the Blood Vessels
For decades, doctors believed migraines were caused by blood vessels in the head expanding and pressing on nerves. That theory has largely been replaced. While blood vessels play a supporting role, a migraine is primarily a neurological event driven by abnormal brain activity and nerve signaling.
The process begins deep in the brain. Imaging studies have shown that a region called the hypothalamus, which regulates sleep, hunger, mood, and body temperature, becomes unusually active up to 24 hours before migraine pain starts. This early brain activity explains why many people experience warning signs like yawning, food cravings, or mood changes well before their head hurts. The hypothalamus also starts communicating abnormally with pain-processing areas in the brainstem, essentially priming the brain’s pain system.
Once triggered, the trigeminal nerve, the main nerve responsible for sensation in your face and head, becomes activated. This nerve releases a signaling molecule called CGRP, which amplifies pain signals and promotes inflammation around blood vessels in the brain’s outer covering. Those pain signals travel through the brainstem up to higher brain regions, producing the intense, throbbing head pain that defines a migraine attack. This is why newer migraine medications work by blocking CGRP from attaching to its receptors, interrupting that pain cascade at its source.
Phase 1: The Warning Signs (Prodrome)
About 24 to 48 hours before the headache hits, many people enter the prodrome phase. This phase can last several hours or stretch over several days, and the symptoms are easy to overlook or attribute to something else.
Common prodrome symptoms include fatigue, irritability, difficulty concentrating, sensitivity to light and sound, nausea, constipation or diarrhea, and muscle stiffness in the neck and shoulders. A few symptoms are especially characteristic of this phase: excessive yawning, cravings for specific foods, and frequent urination. If you notice a pattern where these symptoms reliably show up before your migraines, they can serve as an early alert to take medication or adjust your plans.
Phase 2: Visual and Sensory Disturbances (Aura)
Not everyone gets an aura. For those who do, it typically develops gradually over at least five minutes and lasts up to an hour, though in about 20% of people it can persist longer. The aura usually comes just before or overlaps with the start of head pain.
The most common aura symptoms are visual: geometric patterns, shimmering or flashing lights, zigzag lines, or blind spots that seem to drift across your field of vision. Some people also experience tingling or numbness on one side of the body, or temporary difficulty finding words.
What’s happening in the brain during aura is remarkably well understood. A slow wave of intense electrical activity sweeps across the outer layer of the brain, followed by a prolonged period of suppressed activity. Researchers have measured this wave moving across the visual cortex at roughly 3.5 millimeters per minute. As the wave passes through, it first excites neurons (producing the visual disturbances you see) and then silences them (creating the blind spots). The slow, steady march of this wave is why aura symptoms tend to gradually expand and shift position over several minutes rather than appearing all at once.
Phase 3: The Headache
The headache phase is what most people think of as “the migraine.” It typically lasts from several hours to up to three days. In children and adolescents, attacks tend to be shorter, sometimes lasting as little as two hours.
The pain is usually on one side of the head and has a pulsating or throbbing quality. Routine physical activity like walking up stairs often makes it worse. But the headache is only part of what’s happening. During this phase, your brain becomes hypersensitive to stimulation. Light hurts. Sound hurts. Smells that wouldn’t normally bother you can become unbearable. Nausea is common, and some people vomit. Many find it difficult or impossible to sleep, and anxiety often spikes.
This sensory overload happens because the brainstem, which normally filters and dampens incoming sensory signals, isn’t functioning properly during an attack. Signals that would usually be ignored get amplified instead, which is why a quiet, dark room feels like the only tolerable environment.
Phase 4: The Migraine Hangover (Postdrome)
Once the pain fades, the migraine isn’t necessarily over. The postdrome phase, often called the “migraine hangover,” can last anywhere from a few hours to two full days. Many people describe this phase as feeling like they’ve run a marathon or are recovering from the flu.
Typical postdrome symptoms include fatigue, body aches (particularly a stiff neck), dizziness, light and sound sensitivity, and mood changes that can range from depression to, in some cases, a sense of euphoria. One of the most commonly reported symptoms is mental fog: difficulty concentrating, making decisions, or staying on task. This cognitive impairment can be frustrating, especially for people who assume they should bounce back once the pain is gone.
How a Migraine Is Diagnosed
There’s no blood test or brain scan that confirms a migraine. Diagnosis is based on your pattern of symptoms. The international criteria doctors use require at least five attacks that each last between 4 and 72 hours (when untreated). The headache needs to have at least two of these features: one-sided location, pulsating quality, moderate to severe intensity, or worsening with routine physical activity. You also need to experience nausea, vomiting, or sensitivity to both light and sound during the attack.
These criteria exist partly to distinguish migraines from tension headaches, which tend to affect both sides of the head, feel more like pressure than throbbing, and don’t typically come with nausea or sensory sensitivity. If your headaches don’t fit neatly into these categories, a doctor can help sort out what’s going on.
How Migraine Treatments Work
The two main classes of medication for stopping an active migraine attack work in different ways. Triptans, which have been available since the 1990s, act on specific receptors found on sensory nerves. They’re effective for many people, but because one of those receptors also exists on blood vessels, triptans can cause blood vessel constriction. That makes them a concern for people with heart disease or other vascular conditions.
A newer class of medications called gepants takes a different approach. These drugs block CGRP, the pain-amplifying molecule that the trigeminal nerve releases during an attack, from reaching its receptors. Because they don’t constrict blood vessels, they’re an option for people who can’t safely take triptans. Some gepants can also be taken regularly as a preventive measure, not just during an active attack.
Beyond medication, many people find that identifying and managing their personal triggers, whether that’s irregular sleep, certain foods, hormonal shifts, or stress, reduces how often attacks occur. The brain changes visible on imaging during the prodrome phase suggest that the migraine process starts long before pain appears, which is one reason why early intervention during the warning phase tends to be more effective than waiting until the headache is fully established.