Classification of acne scars into different types based on their appearance ranges from hypertrophic to atrophic. Abnormal wound healing processes have a crucial role in the pathogenesis of scars; however, the exact mechanisms involved in various scar appearances are yet unclear. 

The present study used immunofluorescence and immunohistochemistry techniques to detect the presence of myofibroblasts, B cells and mast cells in each type of acne scar persisting longer than 6 months. 

It found:

• The highest density of myofibroblasts in hypertrophic acne scars, while in the other atrophic scars, it could not identify any myofibroblast-rich areas. 
• Mild B-cell infiltration in only 23% of all acne scar specimens. 
• Mast cells in all specimens, ranging from minimal to high density.
• An association between a high number of mast cells in acne scars and obesity. 

This study shows the abundance of myofibroblasts only in hypertrophic acne scars. Furthermore, mast cells, but not B cells, might play an important role in the pathogenesis of long-standing acne scars.

Source: Chancheewa B, Asawanonda P, Noppakun N, et al. Myofibroblasts, B cells, and mast cells in different types of long-standing acne scars. Skin Appendage Disord. 2022;8(6):469-75.