Medical dermatology is the diagnosis, treatment and prevention of diseases that affect the skin, hair and nails. Dermatology involves study, research, and diagnosis of normal and disorders, diseases, cancers, cosmetic and ageing conditions of the skin, fat, hair, nails and oral and genital membranes, and the management of these by different investigations and therapies, including but not limited to dermatohistopathology, topical and systemic medications, dermatologic surgery and dermatologic cosmetic surgery, immunotherapy, phototherapy, laser therapy, radiotherapy and photodynamic therapy. Dermatologists are medical doctors who deal with skin and skin ailments. Dermatologists specialize in preventing, diagnosing, and treating skin diseases and conditions. Examples of common conditions that they treat include acne, dandruff, and skin cancer. Some dermatologists also perform procedures to improve the appearance of the skin, such as decreasing signs of aging or improving skin tone. These procedures include botox and collagen injections. Dermatologists may also perform minor outpatient surgeries, such as removing legions, warts, moles, or cancerous cells from the skin. Normally, samples of the removed cells are sent off for biopsy.