It sounds like striae also known as stretch marks. Stretch marks begin as darker pigmented marks and fade over time to a silvery colored line. These occur when the dermis is torn due to rapid growth or weight loss. They can be influenced by hormones at puberty and can also occur during pregnancy. There is also a genetic component to stretch marks. They can appear anywhere on the body but most often where fat is stored. The common places are abdomen, breasts, thighs, back, hips, buttocks and upper arms. They are not dangerous or a health risk. Methods to remove them include laser treatments, retinoid creams and dermabrasion.
As my colleague states above, it sounds like you are referring to stretch marks. Stretch marks can be caused by a variety of factors including pregnancy, rapid weight loss or gain, stress, hormonal changes during puberty, hereditary conditions, and changes in physical condition (these can stem from injury through accidents, and even weight-lifting or body-building injuries).
You may be interested in some simple remedies below. Remember that these remedies cannot be substituted for pertinent medical advice. It is always best to consult the proper medical authorities regarding your health concerns. The remedies below may only reduce the appearances of stretch marks.
1) This website lists some natural ingredients such as aloe vera juice, castor oil, lemon juice, and cocoa butter. Drinking plenty of water also helps keep the skin supple and helps restore elasticity of the skin.
2) This website provides a recipe to produce a DIY (Do-It-Yourself) Stretch Mark Cream. Ingredients include olive oil, coconut oil, and Vitamin E oil.
3) This website lists the pros and cons of certain therapies such as:
a) Laser Surgery: this is expensive and must be performed by a doctor. Possible scarring may reduce any cosmetic advantages to this solution.
2) Microdermabrasion: this method uses fine crystals to abrade the skin in order to stimulate collagen production. However, this solution is expensive and the procedure must be done by a qualified and preferably certified physician.
3) Surgical Skin Resection: this method is extremely risky. It involves surgically removing the stretch marks. The process is painful, lengthy and expensive.
4) Stretch Mark Creams: these creams range from store brands to those you can make yourself. All present a whole range of possible cosmetic improvements; some work and others don't. The most effective creams often include those with collagen, liposomes, and elastin in the ingredients.
I hope this helps!