Assessing Acne

9th September 2021

Acne is the most common skin condition which effects up to 95% of adolescents and can occur in up to 43% of adults in their 30’s. 

Despite being more common and severe in male teenagers, it is found to be more frequent and indeed more persistent for adult females. Acne is commonly found on the face with clusters usually on the cheeks, chin and forehead, although it can also effect the back and chest as these anatomic areas also have a high density of hair follicles, hair shafts and sebaceous glands, collectively known as pilosebaceous units. It is caused primarily by inflammation of the pilosebaceous unit, resulting in both inflammatory and non inflammatory lesions.


There a thought to be four main processes in the development of acne: comedones, microcomedones, papules, pustules and nodules, If left untreated, acne can cause scarring, so it is important for practitioners to be able to identify acne in its mildest form to prevent it from worsening and causing scar formation. For this reason it is essential for an accurate assessment to be carried out, and for clinicians to feel competent in doing so.

Acne development, or pathogenesis, takes place in the pilosebaceous unit, which comprises the hair follicle, sabaceous gland and its exit on to the skin surface as a 'skin pore'.
Altered keratinocyte proliferation causes follicular plugs to form at the hair follicle, also known as micro-comedones or whiteheads. These are the target lesion for successful treatment of acne. This process can be further exacerbated by excess sebum production, secondary to androgens during puberty. Other factors thought to play a part in the development of acne include diet, hormonal changes, genetics and drugs.
There are two different types of lesions that practitioners need to be familiar with when assessing acne. The first are inflammatory lesions, which are comedones that can be open (blackheads) or closed (whiteheads) and the second are non inflammatory lesions such as papules, pustules and nodules or cysts. Blackheads are caused by enlarged and stretched pores with a build up of melanin and oil. Papules and pustules are superficial lesions which are raised and less than 5mm in diameter; pustules are fluid filled whereas papules are not. Nodules and cysts are larger than 5mm in diameter.

Types of Acne

Mild Acne - fewer than 20 comedones or less than 15 inflammatory lesions with a total lesion count lower than 30
Moderate Acne - 20-100 comedones or 15-20 inflammatory lesions or a total lesion count of 30-125
Severe Acne - more than five cysts, total comedone count more than 100, or total inflammatory count greater than 50 or a lesion count greater than 125