Acne scars form when the layers of skin under the epidermis become damaged due to a large blemish, whitehead, blackhead or other acne-related lesion. When the skin becomes damaged, excess collagen fibers can form, which can cause an irregular pattern--resulting in a scar. Many commercial creams currently utilize onion extract due to its effect on inflammation. In order to reduce the visibility of these scars, an acne treatment cream containing onion extract may be of benefit.

When applied regularly to an acne scar, onion extract can reduce inflammation in the skin, according to Go Ask Alice. This not only reduces redness that can accompany a newly forming scar, it also can reduce the scar's size. A study conducted on the effectiveness of onion extract conducted by M. Hosnuter, et. al.,published in the June 2007 issue of the "Journal of Wound Care", found that onion extract applied daily to a scar helped to reduce inflammation and discoloration. This is especially beneficial for treating acne scars, which tend to be on the face and are more noticeable when the scarred area is inflamed.

When an acne scar is first forming, excess amounts of collagen fibers can arrange themselves haphazardly on the scar area. This can result in a scar that is raised above the skin or feels hardened. In order to reduce a scar's appearance, it is helpful to reduce the amount of these fibers in order to experience the least damage possible to the skin. Onion extract has been linked with inhibiting collagen production, according to Go Ask Alice. This can help the scar to be smaller in terms of height, according to the American Chronicle, which will help it to appear less noticeable on the face. This benefit is of particular value to those who experience keloid scars, where the collagen over an acne scar multiples and builds, creating a large, raised area over the skin.

Not all acne scars are shaped above the skin--some can become saucer-shaped and lower than the skin, according to DERMA Doctor. In these instances, onion extract creams, such as Mederma, may be utilized to stimulate collagen formation. While the uncontrolled development of collagen is a detriment to a scar, when collagen is encouraged to grow in a more controlled manner, it can make the skin appear most elastic and resilient, which can improve acne scars that are lower than the skin itself.