Conditions · Vitamins and minerals
Pellagra (niacin deficiency) !
Pellagra is lack of niacin: sun-burnt-looking skin, diarrhoea and confusion; untreated it can be fatal.
Updated 2026-11-01
Structures involved
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In biochemistry
- Serotonin and melatonin synthesis: Step 1 · Tryptophan hydroxylase (TPH1 gut and pineal, TPH2 brain)
- Serotonin (5-hydroxytryptamine)
- Niacin (vitamin B3)
In physiology
Why it happens
What it is
A systemic disease of niacin deficiency (or of its precursor tryptophan) that hits the tissues with the fastest turnover or highest energy use: skin, gut lining and brain.
Who gets it
It was epidemic where people ate almost only non-nixtamalised maize (southern Europe and the US in the early twentieth century). Today it is seen with alcoholism, malnutrition, among refugees, and in Africa and Asia on maize or sorghum diets; in Latin America traditional nixtamalisation prevented it.
Causes
- Diet based on non-nixtamalised maize and low in protein
- Chronic alcoholism
- Isoniazid (depletes the B6 needed to make niacin)
- Carcinoid syndrome (the tumour uses up tryptophan)
- Hartnup disease (tryptophan is not absorbed)
- Malabsorption, anorexia nervosa, bariatric surgery
Risk factors
- Poverty and malnutrition
- Alcoholism
- Tuberculosis treatment without pyridoxine
- B2 and B6 deficiencies
Pathophysiology
NAD⁺ and NADP⁺ run short: cells with high turnover and energy demand (keratinocytes, enterocytes, neurons) cannot make enough ATP or repair their DNA, because PARP consumes NAD⁺. Skin exposed to UV light, which damages DNA, becomes inflamed first; the gut lining atrophies (diarrhoea) and neurons fail (encephalopathy).
Symptoms and signs
- Symmetrical dermatitis on sun-exposed skin: backs of the hands, face, neck (Casal necklace)
- Thickened, dark, scaly skin
- Red, smooth tongue, sore mouth
- Diarrhoea, nausea, abdominal pain
- Insomnia, depression, confusion, dementia
Diagnosis
- Clinical
- A clinical diagnosis based on dermatitis, diarrhoea and mental change in someone at risk, confirmed by improvement with niacin.
- Tests
- Low urinary niacin metabolites (N1-methylnicotinamide); tryptophan; screen for other deficiencies, and urine 5-HIAA if carcinoid is suspected.
- Imaging
- Not needed; abdominal CT or other imaging when looking for a carcinoid tumour.
Treatment
- Medical
- Oral nicotinamide until improvement, together with other B-complex vitamins
- Lifestyle
- Diet rich in protein and niacin; nixtamalised maize; treat alcoholism
- Conservative
- Sun protection of affected skin and hydration
- Medical
- Correct the cause: stop or compensate for isoniazid, treat carcinoid or malabsorption
Drugs for this condition
Complications
- Dementia and encephalopathy
- Progressive malnutrition
- Skin infections
- Death without treatment
Prognosis
Mental changes and diarrhoea improve within days; skin takes weeks. It is fatal if untreated.
Prevention
- Nixtamalisation of maize and varied diets
- Pyridoxine with isoniazid
- Flour fortification
Test yourself
Think of the answer, then tap the question to see it.
What are the four Ds of pellagra?
Dermatitis, diarrhoea, dementia and death if untreated.
Why does pellagra affect sun-exposed skin?
UV light damages DNA, and its repair by PARP consumes NAD⁺, which is already scarce.
Why can Hartnup disease cause pellagra?
The gut and kidney neutral amino acid transporter fails, tryptophan is not absorbed and niacin is not made.
What is the Casal necklace?
Band-like dermatitis around the sun-exposed neck, typical of pellagra.
Related conditions
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Pellagra: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Niacin: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Hartnup disease: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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