Strech marks occur when the fibroblasts in your skin revert to a “quiescent” state - i.e. they become dormant and do not synthesise collagen as much as they should. This givers rise to the different skin texture and decreased elasticity, and later, scarring.
There are several treatments. The best is prevention. Adequate dietary fats, Vitamin C, A, E and anti-oxidants will help. Also, using a non-polar body wash (shower milk or something similar) will help prevent stripping of essential oils from the skin and a good emolient will help retain moisture.
Once they occur, various treatments can be used. The most expensive would be some sort of laser work (be careful, a lot of laser practitioners are hippie-scientist charletans). The next most expencive will be an acid peel which you will also have to have done to you.
From a DIY perspective, the only clinically effective treatments are retinoids (Tretionin 10% is the most widely studied and used - can be bought as Retin-A, Ilotycin and a handful of generics). Application of Vitamin E and C have shown promise. Generally a reduction in appearance is achieved but not complete clearing.
IGF1 has also been rumoured to cause general skin repair and may hold a great deal of promise. However, it is a risky drug and is one of the more dangerous BB associated pharmaceuticals.
In due course I will be embarking on my own programme to cure my stretch marks. I will be using Tretinoin, Vit C, Vit E with some sort of transdermal transport mechanism (probably DMSO) and IGF1 administered at low-doses. Will make a post when I am done.