Final answer:
Stretch marks are caused when the skin's dermis is overstretched during rapid growth phases, resulting in tearing of the connective tissue. They typically fade over time but do not disappear completely and are most common on the hips and abdomen.
Step-by-step explanation:
Stretch marks occur when the skin is so extensively stretched that its elastic limits are exceeded. This typically happens during rapid growth phases such as puberty, pregnancy, or with significant weight gain, where the dermis is stretched beyond its capacity to accommodate the excess pressure, causing the underlying connective tissue to tear.
Over time, stretch marks, also known as striae, may fade from a reddish hue to a silvery white color but do not disappear completely. They most commonly appear over areas like the hips and abdomen. Treatment for stretch marks is generally cosmetic, as they do not require medical attention unless they are a part of a larger medical condition.