Stretch marks or striae occur as a result of rapid stretching of skin due to weight changes which leads to elastic and collagen fibres of skin to break. Various treatments are available for reducing the appearance of stretch marks like laser treatments and retinoids( both helps by increasing collagen growth), dermabrasion(helps by increasing skin renewal rate). Some home remedies like application potato juice, aloe vera, lemon juice may help in fading the marks. Consult dermatologist once.