Before the days of biopsies, CT scans and near-instant laboratory tests, doctors relied more on outward signs of disease to arrive at a diagnosis. A thorough history and careful physical exam provided the only clues to disease for early physicians. Technology enhances the physician's diagnostic capability but visible signs of illness still represent the basis for arriving at an initial medical conclusion and guide further workup. An astute physician recognizes signs of certain diseases and disorders, such as the classic skin symptoms of certain vitamin deficiencies.

Niacin

The term "pellagra" derives from the Italian words for rough skin. If you suffer from a niacin -- vitamin B3 -- deficiency, you could develop pellagra. The World Health Organization describes the skin manifestations of niacin deficiency as starting with redness and itching on sun-exposed areas of your skin. Continued lack of vitamin B3 results in the classic dermatitis that almost always leads to the diagnosis. Your skin becomes thickened, dark brown or black, rough and scaly. Hemorrhage and itching can cause a crust to form over the affected areas, which often include a ring around the neck, in a necklace-like distribution. The backs of your hands and your face also commonly display the skin symptoms of niacin deficiency with lesions that are well-delineated from surrounding normal skin.

Vitamin C

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Scurvy remains rare in the United States, but when this severe vitamin C deficiency occurs, such as in malnourished states, the first signs show up on your skin. Initially, red, thickened and raised bumps appear around the hair follicles, especially on your lower legs. As the disease progresses, the bumps seem to grow into each other causing large plaques of discolored skin, says DermNet NZ. The involved areas have a blue or purple discoloration, resembling a bruise, and indicate severe deficiency that likely exceeds several months. MedlinePlus describes bleeding, mostly around the hair follicles and under the nails, as another visible skin sign of vitamin C deficiency.

Vitamin A

Skin lesions give clues to vitamin A deficiency as well, although usually in conjunction with diagnostic eye disorders. As the "Nelson Textbook of Pediatrics" states, if you suffer from a vitamin A deficiency, your skin becomes red, scaly and dry. Patches of thickened, darkened skin appear, especially on the shoulders, buttocks and limbs.

Riboflavin

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If you are deficient in riboflavin, also known as vitamin B2, skin changes include cracking and sores at the corners of the lips. A general dermatitis results as well, with overall skin dryness and itching. Riboflavin deficiency in men can cause a dermatitis-like syndrome of the scrotum with itching and scaling skin.

Many skin symptoms of a vitamin deficiency occur with other disorders as well, so don't rely on the Internet for diagnosis. If you believe you have a vitamin deficiency see your doctor for help with diagnosis and treatment.