Lets see what is an Acne first before going into Acne Scars. Acne refers to lesions or pimples caused when the hair follicles on the skin become plugged with oil and dead skin cells. A plugged follicle is the perfect place for bacteria to grow and create the red bumps and pus-filled red bumps known as pimples. The usual bacteria that causes acne is called Propionibacterium acnes. Hormonal changes during the teen years often cause increased oil production that contributes to the problem.

Causes of Acne Scars
In the simplest terms, scars form at the site of an injury to tissue.
They are the visible reminders of injury and tissue repair. In the case of acne, the injury is caused by the body's inflammatory response to sebum, bacteria and dead cells in the plugged sebaceous follicle.
Two types of true scars exist, depressed areas such as ice-pick scars, and raised thickened tissue such as keloids.
Things to remember before going for Acne Scar removal
People experience different types of scarring from acne, and every person is left with different facial topography. Therefore, acne scar treatment must be addressed on a case by case basis. No single treatment is right for everyone. You and your dermatologist or cosmetic surgeon will have to decide what is right for your type of acne scarring.
Since getting rid of acne scars is a complex process, often several of the treatments listed above will have to be combined to produce the best results. For example, punch techniques followed by laser acne treatments is common. Ice pick acne scars might require undermining the acne scars (subcision) followed by injections (augmentation). It is not uncommon to see more than two procedures combined as well.
Basic research into how acne scars are formed and how they respond to treatment is very limited. It has not been a well treated condition in the past.
Prevention and Treatment of Acne Scars
The best way to prevent post-inflammatory changes caused by acne is to prevent acne lesions from occurring. This is done by understanding the factors that cause acne and using the appropriate treatments for the different acne types.
If you have scarring, the acne scar treatment you get will depend on the type of scars you have, as well as on your skin type. Most experience has been gained treating facial scars. Generally, scars on the chest and back do not respond as well.
Collagen injection. Collagen, a normal substance of the body, is injected under the skin to "stretch" and "fill out" certain types of superficial and deep soft scars. Collagen treatment usually does not work as well for ice-pick scars and keloids.
Autologous fat transfer. Fat is taken from another site on your own body and prepared for injection into your skin. The fat is injected beneath the surface of the skin to elevate depressed scars.
Punch Excision - Ice pick acne scars have hard, irregular jagged borders and often the depth is irregular as well. Simple excision of these scars with a sutured closure allows the dermatologist to bring the dermis back together, get rid of the ragged margins and close the area with a fine, uniform line.
Subcision - In this procedure the dermatologist undermines the acne scar with a sharp instrument such as a tiny scalpel or needle. Subcision helps break fibrous bands of scar tissue that are creating tension between the epidermis and deeper structures and also helps induce new collagen formation.
Dermabrasion - This procedure has fallen somewhat out of favor with the availability of newer, easier to use techniques. In dermabrasion, the skin is anesthetized and frozen and an extremely sharp rapidly rotating blade sheers away damaged tissue.
Laser Treatment. Lasers of various wavelength and intensity may be used to recontour scar tissue and reduce the redness of skin around healed acne lesions.
Skin Surgery. Some ice-pick scars may be removed by "punch" excision of each individual scar. In this procedure each scar is excised down to the layer of subcutaneous fat; the resulting hole in the skin may be repaired with sutures or with a small skin graft. Subcision is a technique in which a surgical probe is used to lift the scar tissue away from unscarred skin, thus elevating a depressed scar.