The four main types of acne are: ● Blackheads - This type of acne is also called open comedones. Blackheads appear when oil and dead skin cells clog hair follicles. The surface of the clogged pore is exposed to air, causing it to darken and appear as a small black spot. ● Whiteheads - Whiteheads are also known as closed comedones. They occur when hair follicles become clogged with oil and dead skin cells, but the surface of the pore remains closed. On the skin, they appear as tiny, white bumps. ● Cysts - Compared to other forms of acne, cysts are large, deep pimples filled with pus. Cysts are caused by hormonal changes or genetics, and they are often painful. ● Nodules - These deep, painful bumps form under the skin and usually last for a few weeks or months. Nodules are often caused by oil and bacteria accumulation in the hair follicles.