Stretch marks
Stretch marks, also known as striae () or striae distensae, are a form of scarring on the skin with an off-color hue. Over time they may diminish, but will not disappear completely. Striae are caused by tearing of the dermis during periods of rapid growth of the body, such as during puberty or pregnancy, in which they usually form during the last trimester. Usually on the stomach, these striae also commonly occur on the breasts, thighs, hips, lower back, and buttocks. Pregnancy-related striae are known as "striae gravidarum". Striae may also be influenced by the hormonal changes  associated with puberty, pregnancy, bodybuilding, or hormone replacement therapy. There is no evidence that creams used during pregnancy prevent stretch marks. Once they have formed there is no clearly effective treatment, though various methods have been attempted and studied. Signs and symptoms. Striae, or "stretch marks", begin as reddish or purple lesions, which can appear anywhere on the body, but are most likely to appear in places where larger amounts of fat are stored; the most common places are the abdomen (especially near the navel), breasts, upper arms, underarms, back, thighs (both inner and outer), hips, and buttocks. Over time , they tend to atrophy and lose pigmentation. The affected areas appear empty, and are soft to the touch. Stretch marks occur in the dermis, the resilient middle tissue layer that helps the skin retain its shape. No stretch marks will form as long as there is support within the dermis; stretching plays a role in where the marks occur and in what direction they run, however, there are a number of contributing factors (see: "Causes", below) to their formation. They can (but do not always) cause a burning and itching sensation, as well as emotional distress. They pose no health  risk in and of themselves, and do not compromise the body's ability to function normally and repair itself, however, they are often considered a cosmetic nuisance. Young women are generally affected the most and often seek treatment for them from a dermatologist and following pregnancy. Causes. Stretch marks appear to be caused by stretching of the skin. This is especially true when there is an increase in cortisone an increase in cortisone levels can increase the probability or severity of stretch marks by reducing the skin's pliability. More specifically, it affects the dermis by preventing the fibroblasts from  forming collagen and elastin fibers necessary to keep rapidly growing skin taut; this can create a lack of supportive material as the skin is stretched, and lead to dermal and epidermal tearing, which in turn can produce scarring in the form of stretch marks. This is particularly the case when there is new tissue growth (which can interfere with the underlying physical support of the dermis or epidermis, by displacing the supportive tissue). Examples of cases where stretch marks are common, also given by the Mayo Clinic, include weight gain (in the form of fat and/or muscle), pregnancy, and adolescent  growth spurts, though it is also noted that some medications, as well as other medical conditions and diseases, may increase the likelihood of stretch marks appearing. In the case of medication, the Clinic points to "corticosteroid creams, lotions and pills and chronic use of oral or systemic steroids" as a common contributing factor. Medical conditions that can contribute to stretch marks include Ehlers-Danlos syndrome, Cushing's syndrome, Marfan syndrome, and "adrenal gland diseases". Pregnancy. Pregnancy stretch marks, also known as "striae gravidarum", are a specific form of scarring of the skin of the abdominal area due to rapid expansion  of the uterus as well as sudden weight gain during pregnancy. About 90% of pregnant women are affected. A number of additional factors appear to promote the appearance of stretchmarks: one study of 324 women, done just after they had given birth, demonstrated that low maternal age, high body mass index, weight gain over 15 kg (33 pounds) and higher neonatal birth weight were independently correlated with the occurrence of striae. Teenagers were found to be at the highest risk of developing severe striae. These skin marks are symptoms of pregnancy caused by the tearing of the dermis, resulting in  atrophy and loss of rete ridges. These scars often appear as reddish or bluish streaks on the abdomen, and can also appear on the breasts and thighs. Some of these striae disappear with time, while others remain as permanent discolorations of the body. Mechanical distension and rapidly developing areas of the body during pregnancy (such as the abdomen, breasts, and thighs) are most commonly associated with striae formation. Some have suggested that relaxin and estrogen combined with higher levels of cortisol during pregnancy can cause an accumulation of mucopolysaccharides, which increases water absorption of connective tissue, making it prime for  tearing under mechanical stress. There also seems to be an association between higher body mass indices and in women with bigger babies and the incidence and severity of striae. Also, younger women seem to be at higher risk of developing striae during pregnancy. The prevalence and severity of striae gravidarum varies among populations. The current literature suggest that in the general population of the US, there is a 50%-90% prevalence of striae associated with pregnancy, partly as a result of the normal hormonal changes of pregnancy and partly due to stretching of skin fibers. Many women experience striae gravidarum during  their first pregnancy. Nearly 45% percent of women develop striae gravidarum before 24 weeks of gestation. Many women who develop lesions during the first pregnancy do not develop them during later pregnancies. Genetic factors such as genealogy and race also seem to be predictive in the appearance of striae. Prevention. Collagen and elastin are proteins in the skin that contribute to the skin's strength, resilience, flexibility, and help skin that has been stretched to recover its original state. Boosting the production of collagen and elastin helps prevent stretch marks from occurring. Stretch marks can also derive from nutritional deficiencies . Consuming foods that contribute to the skin's health, such as zinc-rich foods, foods high in vitamin A, C, D, and protein rich foods, can help suppress stretch marks. A systematic review has not found evidence that creams and oils are useful for preventing or reducing stretch marks in pregnancy. The safety in pregnancy of one ingredient, "Centella asiatica", has been questioned. Evidence on treatments for reducing the appearance of the scars after pregnancy is limited. Treatment. There are no clearly useful treatments for stretch marks, although there are many different suggestions on how to remove them or lessen  their appearance. Various efforts that have been tried including laser treatments, glycolic acid, and microdermabrasion. Tretinoin (0.1% w/w), which is a retinoid, has found to be effective on early stretch marks in several studies. Hyaluronic acid also improves the appearance of stretch marks. Topical tretinoin is categorized by the FDA as a known teratogen (causing malformations in fetuses) in animals, without adequate human studies on safety in pregnancy. Carboxytherapy is a known procedure; however, there is a lack of evidence to support how effective it is. History. Since ancient times, pregnant women have sought remedies to prevent stretch marks  during pregnancy. Both ancient Greeks and Romans used olive oil, while Ethiopians and Somalis used frankincense. Striae were first recognized by Roederer in 1773, and were later histologically described by Troisier and Ménétrier in 1889. In 1936, Nardelli made the first morphologically correct descriptions. Terminology. Medical terminology for these kinds of markings includes striae atrophicae, vergetures, stria distensae, striae cutis distensae, lineae atrophicae, linea albicante, or simply striae.