KnowHOW team explains: The familiar goose egg forms because of the extremely rich supply of small blood vessels in and under the scalp. When they rupture with even a slight bump and the skin is intact, the blood has no place to go, and the pooled blood pushes outward, sometimes to an alarming degree.

The problem can be compounded by an inflammation, so first-aid manuals recommend applying an ice pack wrapped in cloth, or a handy package of something like frozen peas, for about 20 minutes, to ease the pain. The swelling usually goes down in a day or two. The blood may eventually seep downward and cause black eyes.

Because very young children have an even smaller space for the blood to collect, their goose eggs can be especially prominent. Even a newborn often shows a goose egg as the result of the banging around that the head can receive during delivery. It may grow for a week and can take a month or more to dissipate. There is no correlation in either direction between the size of a bump and the seriousness of an injury; a large one can mean that only the scalp tissue was injured, not the underlying bone.

With any head injury, a patient should be observed for at least 24 hours for signs of more serious problems, like confusion, vision problems or unusual drowsiness. Blood un-der the skull has even less room to pool, and its pressure can cause a severe brain damage

The question was sent by Subhash Ghosh from Agartala