Which of the following is not a cause of acne vulgaris?

Acne vulgaris is primarily caused by a combination of factors that lead to the obstruction of hair follicles and the overproduction of sebum. Increased sebum production is a significant factor because the sebaceous glands become overactive, which is often influenced by hormonal changes commonly seen during puberty. Clogged sebaceous glands occur when sebum and dead skin cells build up, leading to the development of comedones, which are the precursors to acne lesions. Additionally, an inflammatory response plays a crucial role in the development of acne, as the blocked follicles can become inflamed and infected with bacteria, leading to the characteristic lesions.

An allergic reaction, however, is not a recognized cause of acne vulgaris. While skin reactions to allergens can manifest in various ways, they do not typically lead to the formation of acne. Acne's development is more directly related to hormonal factors, sebaceous gland function, and inflammation rather than an immune response to an allergen. Hence, this choice accurately identifies a factor that does not contribute to the pathophysiology of acne vulgaris.