Non-inflammatory acne lesions can develop into inflammatory ones when the bacteria present in the skin, Propionibacterium acnes, colonises the hair follicle. That triggers the response of the immune system in the body, meaning that white blood cells are sent there in order to fight the infection. That leads to inflammation and redness of the area. We can differentiate four different types of inflammatory lesions:
Papules: lesions become red and swollen due to inflammation.
Pustules: when the lesions fill with purulent material, containing the whitish or yellowish-looking pus.
Nodules: lesions progress, becoming larger, going deeper into the dermis. They are inflamed and large bumps. They can be very painful.
Cysts: deep and large lesions, filled with pus. When they occur together with nodules, it is called nodulocystic acne.
Acne can also leave secondary lesions like scars and pigmented marks in the area of the lesions
Case of moderate acne with papules and pustules present. Open and closed comedones also present.