Acne is a disease of the hair follicle and sebaceous gland. The sebaceous gland produces an oily substance that drains into the hair follicle. When the neck of the follicle becomes blocked this is the first stage of an acne lesion. Different types of acne lesions reflect the severity of inflammation and the presence of secondary infection. It is important to recognise which types of acne lesions are present as this can help to guide treatment and is an important component of assessing the severity.

Blockage of the hair follicle leads to a collection of keratin (dead skin cells) beneath the opening. When the follicle remains plugged with keratin this is referred to as a whitehead; a blackhead is where the keratin falls out leaving a tiny hole.

Blockage of the hair follicle can lead to inflammation which appears a red spot ‘papule’. This is the classic acne lesion and signifies the presence of inflammatory acne.

More severe inflammation can lead to a tiny collection of pus at the tip of the acne spot. This is a pustule and appears as a tiny white spot.

Persistent inflammation and infection of blocked follicles can lead to the formation of acne nodules and cysts. These are large, red and painful and can result in permanent scarring.