A person’s gender, along with other factors, determines his or her ideal amount of body fat. Women need more body fat than men to maintain their fertility. On average, healthy women have 22% body fat, and healthy men have 14%. To maintain essential body functions, women need at least 12% body fat, but not more than 32%; for men, the range is between 3% and 29%. This difference between females and males is due to the fact that women store more fat on their breasts, hips, and thighs than men do. This difference in muscle mass leads to increased energy use by males, since muscles use more energy than fat does. Women also have an 8% thicker layer of skin under the outer epidermal layer than men. This means that, in a woman and a man of similar strength and body fat, the woman’s muscles would look smoother and less defined than the man’s would. Apart from this, a person’s frame size also influences body fat—larger-boned people carry more fat. In addition, body fat tends to increase with age.