Migraines are caused by abnormal activity in the brain’s pain-signaling network, but the triggers that set off an attack vary widely from person to person. Hormonal shifts, sleep disruption, sensory overload, weather changes, stress, and even caffeine can all play a role. Most of the time, it’s not a single trigger but a combination of factors that pushes the brain past its tolerance threshold.
How a Migraine Starts in the Brain
The pain of a migraine originates in a network called the trigeminal vascular system, which connects pain-sensing nerve fibers to the blood vessels and protective membranes surrounding the brain. When this system is activated, nerve endings release a signaling molecule called CGRP. That molecule triggers a chain reaction: blood vessels dilate, surrounding tissue becomes inflamed, and pain receptors become increasingly sensitized. This process, called neurogenic inflammation, is why migraine pain tends to build and intensify rather than arriving all at once.
The trigeminal nerve has three branches, and the one that covers the forehead, eyes, and the majority of the brain’s protective lining is the branch most involved in migraine. That’s why migraine pain so often concentrates behind or around one eye. About half of the small and medium nerve cells in this system contain CGRP, making it a central player in the pain cascade. Newer migraine medications work by blocking CGRP directly, which is a reflection of how important this single molecule is to the whole process.
The Threshold Theory: Why Triggers Stack
One of the most useful concepts for understanding migraine triggers is the threshold theory. Every person with migraines has an individual tolerance threshold, and it’s rarely one trigger alone that causes an attack. Instead, multiple minor triggers accumulate until they push the brain past that threshold. You might handle a poor night of sleep on its own, for example, but add a skipped meal and a stressful meeting, and you cross the line into a full attack.
This explains why migraines can seem unpredictable. A food or situation that triggered an attack last week might be perfectly fine this week, because the rest of your trigger load was lower. Thinking in terms of cumulative load rather than single causes gives you more practical control over prevention.
Hormonal Shifts, Especially Estrogen
Fluctuating estrogen levels are one of the most well-documented migraine triggers. Steady estrogen levels tend to improve headaches, while sudden drops make them worse. This is why so many women report migraines in the day or two before their period, when estrogen falls sharply.
Pregnancy often brings relief because estrogen rises quickly in the first trimester and stays elevated throughout. But migraines frequently return after delivery, when estrogen drops again. The years leading up to menopause, known as perimenopause, can be particularly difficult. Hormone levels swing unpredictably during this time, and many women find their migraines become more frequent and more severe. Hormonal birth control can go either way: it may smooth out estrogen fluctuations and reduce attacks, or it may make them worse, depending on the individual and the type of contraception.
Sleep Disruption and Circadian Shifts
People with migraines tend to have brains that are unusually sensitive to changes in routine, and sleep is one of the most potent disruptions. A UC Davis study found that even the one-hour shift from daylight saving time was enough to trigger more migraines and reduce deep sleep in participants. The researchers noted that during deep sleep, the brain clears metabolic waste most efficiently, and losing that deep sleep disrupts those clearing mechanisms, potentially creating the conditions for an attack.
Both too little sleep and too much sleep can be triggers. Sleeping in on weekends after a week of sleep debt, jet lag, shift work, or simply an inconsistent bedtime are all common culprits. The underlying principle is that the migraine brain craves regularity.
Sensory Overload: Light, Sound, and Smell
Bright or flickering lights, loud sounds, and strong odors are classic migraine triggers. These aren’t just symptoms that appear during an attack. For many people, they can set one off. Research shows that people with migraines, particularly those who experience aura, have heightened activation in the visual cortex in response to light compared to people without migraines. Their brains are, in a measurable sense, more reactive to sensory input even between attacks.
This heightened reactivity means that fluorescent lighting, screen glare, concert-level noise, or heavy perfume can act as genuine triggers. The mechanism connects back to the trigeminal system: intense sensory input can lower the threshold of pain-processing neurons, making the brain more vulnerable to a full attack.
Weather and Barometric Pressure
Changes in barometric pressure are a recognized migraine trigger, though the exact mechanism isn’t fully understood. The leading explanation is that pressure shifts cause imbalances in brain chemicals, including serotonin, which helps regulate pain signaling. Storms, rapid temperature swings, and high humidity are the weather patterns most commonly reported as triggers.
Weather is a frustrating trigger because you can’t control it. But knowing it’s a factor can help you manage your other triggers more carefully on days when a pressure change is forecast, keeping your overall load below that threshold.
Caffeine: Both Remedy and Trigger
Caffeine has a complicated relationship with migraines. In small or occasional doses, it narrows blood vessels around the brain and can actually relieve headache pain. It’s an ingredient in many over-the-counter pain relievers for exactly this reason: it increases the absorption and effectiveness of the medication.
The problem starts with regular use. When your brain adapts to daily caffeine, skipping it causes blood vessels to widen again. That increased blood flow puts pressure on surrounding nerves and triggers what’s known as a rebound or withdrawal headache. This can happen within hours of your usual coffee time. Even a change in timing, like sleeping past your usual first cup, can be enough. If you consume caffeine regularly, consistency matters more than the amount.
Food, Fasting, and Dehydration
Skipping meals is one of the most commonly reported migraine triggers. The drop in blood sugar appears to stress the brain enough to initiate an attack in susceptible people. Dehydration works similarly, reducing blood volume and altering the chemical balance the brain relies on.
Specific foods are trickier. Aged cheeses, processed meats, alcohol (especially red wine), and foods containing MSG are frequently cited, but the evidence for individual food triggers is inconsistent across studies. What’s more reliable is the pattern of irregular eating. Going long stretches without food or fluid is a more dependable trigger than any specific ingredient for most people.
Stress and the Letdown Effect
Stress itself is a well-known trigger, but many people find that migraines actually hit after the stressful period ends. This “letdown effect” often explains weekend migraines or attacks that arrive on the first day of a vacation. The body’s stress hormones, which may have been suppressing the attack during the crisis, drop off, and the migraine emerges.
This makes stress management particularly nuanced for people with migraines. Abruptly shifting from high stress to complete relaxation can be just as destabilizing as the stress itself. Gradual wind-downs, consistent sleep schedules through weekends, and steady routines help more than dramatic shifts between tension and relief.
Genetics and Family History
Migraines run strongly in families. If one or both of your parents have migraines, your risk is significantly higher. The genetic component is clearest in a rare form called familial hemiplegic migraine, where mutations in specific genes disrupt how ions move across nerve cell membranes. That disrupts the normal release and uptake of neurotransmitters in the brain, essentially making the signaling system unstable.
These specific gene mutations don’t appear to play a major role in common migraines, which affect a far larger population. But the broader principle holds: genetics determine how excitable your brain’s nerve cells are, and that excitability sets your baseline vulnerability. Your genes set the floor. Your triggers determine whether you cross it on any given day.