Middle age is the period of a human's life beyond young adulthood but before the onset of old age or "third age". The exact range is subject to academic debate, but commonly the term is used to denote the age range from around the mid 40s until around the mid 60s, although it may begin earlier and end later. This phase of life is marked by gradual physical, cognitive, and social decline in individuals as they age. Middle adulthood This time span can be referred to as "middle age" and can be defined as the time of ages about 40+ to about 60+, even depending on sexes. Many changes may occur between young adulthood and this stage. Some definitions start later, at around age 45, such as those of Merriam-Webster and the Oxford English Dictionary. Some start as late as age 50. There is no universal consensus on what the exact definition of middle age is, but usual characteristics include the beginning of rapid decline of fertility, graying of hair, and lessening of opportunities. The American Psychological Association defines "middle adulthood" as beginning at 35 or 36, and many ranges do not end until 60 or 65. The Lancet considers midlife as starting from around age 40. Modern social scientists generally agree that midlife begins around 35 to 40 and ends around 55 to 60. The body may slow down and the middle aged might become more sensitive to diet, substance abuse, stress, and rest. Chronic health problems can become issues along with disability or disease. Emotional responses and retrospection vary from person to person; for example, senses of mortality, sadness, or loss are common emotions at this age. Those in middle adulthood or middle age continue to develop relationships and adapt to changes in relationships. Such changes are highly evident in the maturing relationships between growing or grown children and aging parents. Community involvement is fairly typical of this stage of adulthood, as is continued career development. Physical characteristics Middle-aged adults may begin to show visible signs of aging. This process can be more rapid in women who have osteoporosis. Changes might occur in the nervous system. The ability to perform complex tasks remains intact. During the years surrounding the age of 51, women experience menopause, which ends natural fertility. Menopause can have many side effects. Changes can occur to skin, and other changes may include a decline in