Stress does not wait for a convenient moment. It hits in elementary school, in a college dorm room, in the middle of finals, and sometimes in the middle of an ordinary bad day. What changes is not the feeling itself, but the way people reach for comfort. For younger children and first-semester college students alike, a growing body of research points to something simple and familiar: hearing from family, especially a mother, can help take the edge off. That idea may sound sentimental, but several studies described by researchers suggest it has measurable effects in the body as well as in daily life. When a mother’s voice changes the chemistry of stress One experiment led by Seth D. Pollak, a psychology professor at the University of Wisconsin-Madison, focused on girls between about 7 and 12 years old. To create a stressful situation, researchers had them give a speech or solve math problems in front of an audience, the sort of setup that can rattle even confident adults. One study focused on girls between about 7 …