The incidence of scarring in acne is not known. It is frequently stated that acne scarring results from severe inflammatory nodulocystic lesions occurring deep  in the dermis. Some patients, however,  scar without having had significant nodulocystic acne; the scarring can arise from more superficial inflamed lesions. Because of the variability in  scarring in different subjects with similar  inflammatory lesions, it  is  likely that some patients may be  more prone than others to develop scarring.

  The life history of acne scars is also not known. We are all aware of subjects who still, many years after the acne has resolved,  continue to  demonstrate what, at times,  may be  psychologically  distressing  scars. However, there are some subjects who  consider that they did have acne quite badly, resulting in scarring, but which has, over the years, improved. This suggests that there is sometimes,  with time, remodelling of the skin. Although this is a useful fact to relay to patients in order to encourage them about the longterm appearance of their skin, these events require further careful attention before we can be really certain about the ultimate resolution, if any, of acne scars. It would be worthwhile to undertake a detailed investigation of the development of scars, in  terms of their onset, their type and their possible improvement over time.

  There are fundamentally two types of tissue response in acne scarring. One is increased tissue formation; the other is loss of tissue. Increased tissue formation Hypertrophic and keloid scars   The distinction between  hypertrophic scars  and  keloid  scars is often vague. In theory, the former do not extend beyond the site of original skin damage but rarely does the physician see, or the patient remember,  the extent of the original inflammatory lesion. Both hypertrophic scars  and keloid scars  are associated with increased collagen. They present as firm, smooth, usually irregularly shaped lesions - fleshor pink-coloured:  although some may be 1-2 mm in diameter, others may reach 1 cm or more. The large ones tend to be linear rather than oval. Keloids are most frequently  seen on the upper trunk. The commonest site on the  face is around the angle of the jaw; they are uncommon on the forehead and upper cheek. Loss of tissue Scars associated predominantly with loss of tissue are more common.  In this category are considered ice-pick scars, depressed fibrotic scars, superficial and deep soft scars, atrophic macules and follicular macular atrophy. Ice-pick scars   Ice-pick scars  may be superficial or deep, and commonly occur on the cheeks.  They are usually fairly small, linear but irregular and  with a somewhat jagged edge, sharp margins and steep sides. They may be soft or hard; the latter usually have a firm fibrotic base and, in contrast to the soft ice-pick scars, cannot be easily stretched. This is an important practical  point in  that the scars which  are usually more superficial may  be helped with the injection of bovine collagen. Depressed fibrotic scars   Depressed fibrotic scars are usually quite  large    and, like  ice-pick scars, have sharp margins and steep sides. The base is firm and white and they cannot be distended. Superficial and deep soft scars   Superficial and deep soft  scars are of variable  depth,  distensible  and have gently sloping rolled  edges  merging into normal skin . They are small and are either circular or linear in shape. Atrophic macules  Atrophic macular  scars may be a few millimetres in diameter, especially  on the face, but on the  upper trunk often reach  up to 1 cm or more . They are soft and distensible  and their base, which  is often finely wrinkled,  tends to have a violaceous hue, presumably due to the ease with which the underlying vessels are seen. With time they become ivory-white in colour and so are much less obvious. Follicular macular atrophy   Follicular macular atrophy (FMA)  is rare on the face but these lesions are present in small numbers on the trunk of many acne patients. These are usually so inconspicuous that they are  not  noted by the patient or physician. However, they can occasionally be sufficiently extensive to be the primary cause of referral. The term FMA is probably  identical to  'perifollicular elastolysis'.

  Clinically, FMA consists of small, white, perifollicular  lesions which are soft and often just palpable above the skin surface. They occur equally in both sexes and are related to the duration and severity  of the acne. Histologically there is marked loss  of elastic tissue around the follicle. Limited clinical evidence  suggests that many of these lesions are  aborted whiteheads. diffraction analysis showed that the crystalline component is hydroxyapatite,12 a primary constituent  of the bone. Perhaps the most important aspect of post-acne calcification is the fact that it can enter the differential diagnosis of shadowing on an X-ray.13 Calcification of scars A rare  complication  of acne scarring  is calcification ,  to the  extent  of producing  osteoma cutis.10 In most cases of post-acne osteoma cutis there is no visible or palpable evidence of calcification. More rarely, the disorder presents as  small, palpable,  pigmented nodules. In a case of the latter type,  X-ray.