What are migraine headaches? A migraine is a very bad headache that tends to come back over and over again. Migraine attacks can be as often as once or twice a week. The sufferer may feel sick and may vomit. The pain is usually on one side of the head and sufferers often experience visual disturbances, such as seeing flashes or spots or having double vision. People who are experiencing a migraine may be very sensitive to bright lights and noise. Moving around makes the headache even worse. Migraine is a disease, just like diabetes and heart disease, and requires medical attention. Three out of four migraine sufferers are female. Some migraine cases are hereditary. Doctors believe migraines may be caused by a chemical or electrical problem in certain parts of the brain. Some things can cause a migraine or make it worse, including stress and anger, smells, fumes, weather changes, too much or too little sleep, hunger, excessive activity and medications that cause blood vessels to swell. Some foods may also trigger a migraine. Alcohol, coffee, chocolate, dairy products and monosodium glutamate (MSG), which is often found in Chinese food, can cause migraines. Medicine can be taken to prevent migraines or to stop the pain and nausea. What are bulletproof vests made of and how do they work? Most bulletproof vests are made of a fabric woven from Kevlar, a synthet ic fibre. The fibre's chemical composition gives it a strength greater than steel. Kevlar's strength keeps it from breaking when the bullet hits, and the weave of the fabric serves to absorb and distribute the energy of the bullet's impact. If a bullet struck a vest woven from cotton fibres, for example, the fibres would break under the bullet's impact, allowing the bullet through, with unpleasant results for the wearer. The reason Kevlar fibres can keep a bullet out is their tremendous strength. A Kevlar fibre is five times as strong as a steel fibre of the same weight. The weave of the fabric also helps to distribute the energy of the impact across the entire vest, sparing the person wearing the vest from being injured by the force of the bullet's impact. The vests are classified according to the type of bullets they can stop. The classes differ in the number of layers of Kevlar fabric they contain. The light weight and flexibility of the Kevlar vests makes them routinely used by police and security forces in dangerous situations. But while it will stop hand-gun bullets, Kevlar fabric is no match for high-powered rifle fire. To stop those bullets takes steel plate or ceramic vests that weigh four kilograms or more.