What Scar Type Do You have?
If you have depressed scarring then you can benefit from collagen injections to raise the atrophic levels of the skin so that the surface is flat. For hypertrophic conditions such as Keloid acne scars, collagen is not the right treatment for you.
How does it work?
Collagen acts as an injectable filler that raises the level of the depressed tissue so that the surface is smooth. The effect of this is a massive improvement in aesthetics with scar notice-ability reducing significantly.
This technique is best used with scars that are not very deep but numerous.
How long does it last for?
Unfortunately this solution to scarring isn't permanent and you can expect the benefits of the injections to last roughly 9 months to a year before more injections will be required.
How much does it cost?
In comparison to other scarring treatments, collagen injections are very cheap. You can expect to pay around $125 for a series of injections.
Limitations
Deep ice pick scars do not do well with collagen injections, a better treatment for this type of scar would be something like chemical peels, dermabrasion or laser resurfacing.
source:
http://ezinearticles.com/?Collagen-For-Acne-Scars&id=3358515