Skin Health Acne Causes & Risk Factors What Causes a Pimple? How Acne Breakouts Develop By Angela Palmer facebook Angela Palmer is a licensed esthetician specializing in acne treatment. Learn about our editorial process Angela Palmer Medically reviewed by Medically reviewed by Casey Gallagher, MD on May 19, 2020 Casey Gallagher, MD, is board-certified in dermatology. He is a clinical professor at the University of Colorado in Denver, and co-founder and practicing dermatologist at the Boulder Valley Center for Dermatology in Colorado. His research has been published in the New England Journal of Medicine. Learn about our Medical Review Board Casey Gallagher, MD on May 19, 2020 Print Acne is a chronic disorder of the sebaceous glands. While sometimes it seems pimples appear overnight, the development of an acne breakout is actually an extended process that begins at the cellular level. All pimples begin as a blockage of the hair follicle, or pore. Gaining an understanding of why a blockage begins and how a pimple develops will ultimately help you in treating your acne. Jose Luis Pelaez Inc / Getty Images The Epidermis The outermost section of the skin, the part you see every day, is called the epidermis. The epidermis consists of five layers. The deepest layer of the epidermis is the stratum germinativum. It is composed of a single layer of cells. Cell division, or mitosis, takes place in the stratum germinativum. The new cells begin their journey up through epidermis to the skin's surface. First, they are pushed up through the stratum mucosum, then the stratum spinosum. These three layers (stratum germinativum, mucosum, and spinosum) together are called the basal layer. As the skin cells travel further, they reach the stratum granulosum. In this layer, the cells begin dying and hardening, giving them a granular appearance. By the time the cells reach the stratum corneum, they are dead. The stratum corneum is made up of these tightly packed dead skin cells, which are continuously falling off and being replaced. This process is called desquamation. It takes approximately 28 days, from cell birth to sloughing off, to occur. The Dermis The dermis is the deepest, or inner section, of your skin and is made up of tough connective tissue. The dermis nourishes and supplies blood to the epidermis. It is also what gives the skin its elasticity. The dermis is much thicker than the epidermis but has just two distinct layers: the papillary layer and the reticular layer. Within the dermis, you will find blood and lymph vessels, nerves, arrector pili muscles (the muscles that make your hair stand on end), sudoriferous (sweat) glands, sebaceous (oil) glands, and hair follicles. It is within the hair follicle and sebaceous glands that acne begins. The Hair Follicle The hair follicle is a small, tube-like opening in the skin through which hair and sebum reach the skin's surface. The follicle consists of the pore opening, hair root and bulb, sebaceous duct, and sebaceous gland. Although it is contained within the dermis, the epidermis lines the inside of the hair follicle. In a normal functioning follicle, the sebaceous glands secrete oil, or sebum, into the pore. Typically, sebum and dead cells shed from the stratum corneum emerge at the skin's surface through the pore opening. In those with acne, however, this process goes awry. In acne-prone skin, sebum and dead skin cells easily become trapped within the follicle. This accumulation of cellular debris and sebaceous matter forms a hard plug that obstructs the pore opening. This obstruction is called a comedo. It manifests itself as non-inflamed bump or blackhead on the skin's surface. Propionibacteria Acnes Propionibacterium acnes (P. acnes) is the bacterium responsible for inflamed acne breakouts. P. acnes are regular residents within the hair follicle. Normally, they are harmless. However, in acne prone skin the P. acnes population grows out of control. When a comedo blocks the pore opening, it creates an anaerobic environment or a lack of oxygen within the follicle. This anaerobic environment, along with excess sebum within the pore, creates a favorable environment where P. acnes bacteria can thrive. As the follicle becomes filled with sebum, dead cells, and bacteria, it begins to swell. The follicle wall ruptures and spills into the dermis. White blood cells rush in to fight the bacteria. Redness and swelling occur, and pus is created. A pimple has now formed. If the rupture in the follicle wall happens near the surface, the pimple is usually minor and heals quickly. It is when the break occurs deep within the dermis that more severe lesions, such as nodules and cysts, develop Was this page helpful? Thanks for your feedback! Dealing with acne can be frustrating. Our free guide provides expert tips to help you take control. Sign up and get yours today. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. National Institute of Arthritis and Musculoskeletal and Skin Diseases. Acne. Yousef H. Anatomy, Skin (Integument), Epidermis. StatPearls [Internet]. June 2019. Perry A, Lambert P. Propionibacterium acnes: infection beyond the skin. Expert Rev Anti Infect Ther. 2011;9(12):1149-56. doi:10.1586/eri.11.137 Additional Reading National Health Service. Acne.