Stretch marks (Striae distensae)

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What is Stretch marks?

Stretch marks (also known as striae distensae) are part of a condition affecting the skin, and are commonly found in the population. These white, smooth, linear lesions can be found anywhere on the body and are related to stretching of the skin. The most common sites to be affected by stretch marks include the breasts, buttocks, thighs and lateral abdomen. Stretch marks appear to be a type of scarring that occurs in the dermal layer of the skin, as a result of an altered healing response and replacement of collagen. They are separated from the normal skin by dense collagen bundles. The following image shows the side of a patient's thigh, which has been affected by stretch marks. The red colouring indicates that the stretch marks are of recent onset. The appendages normally present in skin - including hair follicles, sweat glands and other structures are absent in areas affected by stretch marks.

Who gets Stretch marks?

Depending on the race and age of the population studied, the prevalence of stretch marks has been reported to range from 50% to 90%. Due to the introduction of techniques such as in vitro fertilisation, the ability of women to reproduce has been lengthened, and the age of onset of stretch marks can vary greatly. Many women develop stretch marks during their first pregnancy. One study demonstrated that 43% of the women enrolled developed stretch marks before 24 weeks of gestation. It is unknown why some women are not affected; a recent study, strongly suggests that your family history and genetics may play a role.

Predisposing Factors

The cause of stretch marks appears to be a decrease in elastin fibers and fibrillin in the dermal layer of the skin. The orientation of these fibers also changes from the normal pattern (at right angles to the skin layer junctions) to an abnormal parallel pattern. This is closely related to hormonal and physical factors. Stretch marks are commonly found to affect many people, especially with conditions such as Cushing's syndrome, pregnancy and prolonged use of steroid medications.

There is also a familial predisposition to stretch marks. Non-white women and women with a history of breast or thigh stretch marks are more prone to developing stretch marks during pregnancy. Other factors, such as race and increasing age, are also found to be predictive.

Common predisposing circumstances for the devlopment of stretch marks include; those which involve a physical stretching of the skin, such as rapid weight gain or adolescent growth spurts, and others that involve hormonal changes, such as chronic steroid medication use or Cushing's syndrome.

Progression

Regardless of their causes, all stretch marks follow a natural course of progression. Active lesions are the early lesions that consist mainly of fine elastic fibers. As the stretch marks age, the fibers become thicker and there is a decrease in the thickness of the dermal layer of the skin.

However, different people are affected by stretch marks differently and the severity and development of lesions appear to depend greatly on individual factors. Once again, this suggests a genetic component.

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