Dermatology is the branch of medicine dealing with the skin , nails , hair and its diseases .  It is a specialty with both medical and surgical aspects.    A dermatologist treats diseases, in the widest sense,  and some cosmetic problems of the skin, scalp, hair, and nails. 
Readily visible alterations of the skin surface have been recognized since the dawn of history, with some being treated, and some not. In 1801 the first great school of dermatology became a reality at the famous Hôpital Saint-Louis in Paris, while the first textbooks (Willan's, 1798–1808) and atlases ( Alibert's , 1806–1814) appeared in print during the same period of time.
After earning a medical degree ( M.D. or D.O. ), the length of training in the United States for a general dermatologist to be eligible for Board Certification by the American Academy of Dermatology, American Board of Dermatology or the American Osteopathic Board of Dermatology is a total of four years. This training consists of an initial medical, transitional, or surgical intern year followed by a three-year dermatology residency.    Following this training, one- or two- year post-residency fellowships are available in immunodermatology , phototherapy , laser medicine , Mohs micrographic surgery , cosmetic surgery or dermatopathology . For the past several years, dermatology residency positions in the United States have been one of the most competitive to obtain.   
In the UK, a dermatologist is a medically qualified practitioner who has gone on to specialise in medicine and then sub-specialise in dermatology. This involves:
-Medical school for five years to obtain an MBBS, MBBCh or MB,BChir degree
-One year of house jobs (Foundation year 1) before becoming fully registered as a medical practitioner
-Two to three years training in general medicine (Foundation years 2 and 3 or more) to obtain a higher degree in medicine and become a member of the Royal College of Physicians
-Having obtained the MRCP examination, applying to become a Specialty Registrar (StR) in Dermatology and training for four years in dermatology.
-Passing the Specialty Certificate Examination (SCE) in Dermatology before the end of training
-Upon successful completion of the four-year training period, the doctor becomes an accredited dermatologist and is able to apply for a consultant hospital post as a consultant dermatologist.
Dermatologists have been leaders in the field of cosmetic surgery. Some dermatologists complete fellowships in surgical dermatology. Many are trained in their residency on the use of botulinum toxin , fillers, and laser surgery. Some dermatologists perform cosmetic procedures including liposuction , blepharoplasty , and face lifts .   Most dermatologists limit their cosmetic practice to minimally invasive procedures. Despite an absence of formal guidelines from the American Board of Dermatology , many cosmetic fellowships are offered in both surgery and laser medicine.
A dermatolopathologist is a pathologist or dermatologist who specializes in the pathology of the skin. This field is shared by dermatologists and pathologists. Usually a dermatologist or pathologist will complete one year of dermatopathology fellowship. This usually includes six months of general pathology, and six months of dermatopathology.  Alumni of both specialties can qualify as dermatopathologists. At the completion of a standard residency in dermatology, many dermatologists are also competent at dermatopathology. Some dermatopathologists qualify to sit for their examinations by completing a residency in dermatology and one in pathology.
This field specializes in the treatment of immune-mediated skin diseases such as lupus , bullous pemphigoid , pemphigus vulgaris , and other immune-mediated skin disorders. Specialists in this field often run their own immunopathology labs.
The dermatologic subspecialty called Mohs surgery focuses on the excision of skin cancers using a tissue-sparing technique that allows intraoperative assessment of 100% of the peripheral and deep tumor margins developed in the 1930s by Dr. Frederic E. Mohs . The procedure is defined as a type of CCPDMA processing. Physicians trained in this technique must be comfortable with both pathology and surgery, and dermatologists receive extensive training in both during their residency. Physicians who perform Mohs surgery can receive training in this specialized technique during their dermatology residency, but many will seek additional training either through preceptorships to join the American Society for Mohs Surgery  or through formal one- to two-year Mohs surgery fellowship training programs administered by the American College of Mohs Surgery. 
This technique requires the integration of the same doctor in two different capacities: surgeon as well as pathologist. In case either of the two responsibilities is assigned to another doctor or qualified health care professional, it will not be considered to be Mohs surgery.
Physicians can qualify for this specialization by completing both a pediatric residency and a dermatology residency. Or they might elect to complete a post-residency fellowship.  This field encompasses the complex diseases of the neonates , hereditary skin diseases or genodermatoses , and the many difficulties of working with the pediatric population.
Teledermatology is a form of dermatology where telecommunication technologies are used to exchange medical information via all kinds of media (audio, visual and also data communication, but typically photos of dermatologic conditions) usually made by non-dermatologists for evaluation off-site by dermatologists).  This subspecialty deals with options to view skin conditions over a large distance to provide knowledge exchange ,  to establish second-opinion services for experts  or to use this for follow-up of individuals with chronic skin conditions.  Teledermatology can reduce wait times by allowing dermatologists to treat minor conditions online while serious conditions requiring immediate care are given priority for appointments. 
Dermatoepidemiology is the study of skin disease at the population level.  One aspect of dermatoepidemiology is the determination of the global burden of skin diseases.   From 1990 to 2013, skin disease has constituted approximately 2% of total global disease disability  as measured in disability adjusted life years (DALYS). 
Therapies provided by dermatologists include, but are not restricted to the following:
- Cosmetic filler injections
- Hair removal with laser or other modalities
- Hair transplantation – a cosmetic procedure practiced by many dermatologists.
- Intralesional treatment – with steroid or chemotherapy .
- Laser therapy – for both the management of birth marks, skin disorders (like vitiligo ), tattoo removal , and cosmetic resurfacing and rejuvenation.
- Photodynamic therapy – for the treatment of skin cancer and precancerous growths.
- Phototherapy – including the use of narrowband UVB, broadband UVB, psoralen and UVB.
- Tattoo removal with laser.
- Tumescent liposuction – liposuction was invented by a gynecologist . A dermatologist (Dr. Jeffrey A. Klein ) adapted the procedure to local infusion of dilute anesthetic called tumescent liposuction. This method is now widely practiced by dermatologists, plastic surgeons and gynecologists. 
- Cryosurgery – for the treatment of warts, skin cancers, and other dermatosis.
- Radiation therapy – although rarely practiced by dermatologists, many dermatologist continue to provide radiation therapy in their office.
- Vitiligo surgery – Including procedures like autologous melanocyte transplant, suction blister grafting and punch grafting.
- Allergy testing – 'Patch testing' for contact dermatitis.
- Systemic therapies – including antibiotics, immunomodulators, and novel injectable products.
- Topical therapies – dermatologists have the best understanding of the numerous products and compounds used topically in medicine.
Most dermatologic pharmacology can be categorized based on the Anatomical Therapeutic Chemical Classification System , specifically the ATC code D .