Stretch marks are caused by exactly what their name suggests - stretching. The skin's natural elasticity is provided by collagen and elastin in the dermis. Collagen and elastin are made up of proteins and are key components of the body's connective tissue. This connective tissue enables the dermis to adapt to continuous movement of the body by expanding and contracting as it changes. During periods of sudden weight gain or loss the skin may have insufficient time to adjust, causing internal tears in the skin tissue which form the scars known as stretch marks.

The likelihood of developing stretch marks varies according to skin type, age, heredity, diet and hydration of the skin. Typically, stretch marks tend to occur under the following conditions:

Puberty. As the adolescent body goes through rapid growth cycles stretch marks can develop.

Pregnancy. Stretch marks are common during the later stages of pregnancy as the abdomen expands to accommodate the growing baby.

Rapid weight gain/muscle growth. If weight or muscle mass is significantly increased over a short period of time stretch marks may become apparent.

Certain medical conditions. Stretch marks can be a symptom of an underlying medical condition such as Cushing's syndrome and Marfan syndrome. Cushing's syndrome causes stretch marks by overproduction of the hormone cortisol which weakens the skin. Similarly, Marfan syndrome causes stretch marks as it weakens the body's connective tissue due to a defective gene. Ehlers-Danlos syndrome (EDS) is a rare inherited condition that affects structural proteins, weakening connective tissue in the skin which can also cause stretch marks. 


The skin consists of three key layers: epidermis (the outer layer), dermis (the middle layer) and subcutaneous or hypodermis (the deepest layer). Usually, as the body grows, the strong connecting fibers in the dermis slowly stretch. However, stretch marks form in the dermis when the connective tissue is stretched beyond its natural elasticity, causing fibers in the dermis to tear allowing deeper skin layers to show through. It is when these tears repair themselves, they form the scars known as stretch marks. Typically, there are three distinct stages in stretch mark formation: 

Stage one. Early stretch marks develop in a pale red/purple colour and may also be itchy. The skin immediately around the stretch marks may also appear thin and flattened.

Stage two. As the skin continues to stretch, gradually the stretch marks will expand in length and/or width, becoming darker in colour and more pronounced as blood vessels begin to show through tears in the dermis.

Stage three. When the skin is no longer under tension the stretch marks will mature and start to fade. Eventually, they develop a silver or white appearance as the blood vessels contract and the pale fat underneath the skin becomes visible instead. Late-stage stretch marks may appear slightly depressed and irregular in shape.