Vitamin B3 (niacin) deficiency symptoms usually start with a rash on sun-exposed skin that looks like sunburn, a sore red tongue and gut trouble, then move to confusion if nothing changes. Severe deficiency is called pellagra, and doctors still teach it as the four Ds: dermatitis, diarrhoea, dementia and death.
The catch is that the textbook version rarely turns up in full. In one Indian addiction centre, only 19% of pellagra patients had diarrhoea. Every one of them had the rash. So the useful question is which signs show up, and who should be looking for them.
The short version
- Severe B3 deficiency is pellagra: rash, gut trouble, confusion, and it can kill.
- The rash appears on sun-exposed skin and looks like a slow sunburn.
- Most patients never show all three classic signs at once.
- Heavy drinking, the TB drug isoniazid and carcinoid tumours are the main modern causes.
- Men need about 16.5mg a day, which a normal mixed diet covers.
Here are the 7 signs, roughly in the order a clinician would spot them.
1. A rash that behaves like sunburn
The skin is the giveaway. Pellagra is generally accepted as the first photosensitivity syndrome described, and the rash sits on the parts of you the sun hits: backs of the hands, forearms, face, neck and the tops of the feet.
It starts red and sore. A 2004 review in the International Journal of Dermatology describes acute pellagra as resembling sunburn early on, except it tans more slowly than a normal burn and flares again every time the skin goes back into the sun. Over time the skin darkens. The 2011 British Journal of Dermatology review calls it an exposed-site hyperpigmented dermatitis.
Symmetry is the tell. A burn from one afternoon in the garden doesn't usually come back the same way on both forearms every sunny day.
2. A ring of rash around the neck
One pattern is distinctive enough to have its own name. Casal's necklace is a dark band of rash around the neck where the collar line meets sun exposure. It still turns up in case reports, including a homeless man in Lisbon whose pellagra presented as a psychiatric illness.
If you see that band alongside a sunburn-style rash on the hands, B3 moves to the top of the list.
3. A sore, red tongue and mouth
The mouth often joins in. A systematic review of pellagra in anorexia nervosa lists glossitis (a swollen, smooth, red tongue) and stomatitis (sores and cracking in the mouth) among the most common features, alongside the sun-exposed rash.
A sore tongue on its own is not specific. Other B vitamin gaps can cause one too, so the B12 deficiency signs overlap with this list.
4. Diarrhoea and a gut that won't settle
The second D is the gut. The 2021 Krak�w review lists gastrointestinal symptoms as one of the three main groups of pellagra signs, and diarrhoea is the classic one.
It is less reliable than people expect. In the review of 2,947 alcohol-dependence admissions in Bangalore, 31 patients (1%) had pellagra. All 31 had dermatitis, but only 19% had diarrhoea.
5. Confusion, delirium or a sudden change in mood
The third D was originally "dementia", but that undersells how fast it can move. A Boston case series argues the brain picture is better described as delirium, and that pellagra can present as delirium with no rash and no gut symptoms at all.
In the Bangalore records, 58% of pellagra patients had delirium. A 2014 review in Alcohol and Alcoholism reports a patient with delusions and visual hallucinations who recovered on niacin, and the authors say pellagra should still be considered when a heavy drinker develops acute psychosis.
This is the dangerous part. It gets mistaken for alcohol withdrawal, and the withdrawal guidelines the Boston team reviewed didn't list pellagra as a possibility.
6. Fatigue and vague symptoms that come first
Before any of the above, there is usually a slow phase that nobody connects to a vitamin. The same systematic review notes that nonspecific symptoms build up quietly before the classic signs appear, affecting the skin, the gut and the nervous system.
In practice that means tiredness, low mood, headaches and poor appetite. None of those point to B3 on their own. Plenty of things cause them, and a dozen nutrient gaps sit on that list before niacin does.
So treat this one as context, not a diagnosis. If you also fit the risk list further down, it is worth mentioning to your GP.
7. The full triad usually doesn't show up
This is the one that catches doctors out. The textbook teaches three signs together, but the Boston authors found pellagra "seldom presents with all three findings", and the Bangalore team concluded the classical triad is only seen in a minority of cases.
The Krak�w review adds that because the disease is now rare, most physicians are unfamiliar with it, which often delays diagnosis. If you wait for all three Ds, you wait too long.
Who actually gets vitamin B3 deficiency
For a healthy man eating meat, fish, eggs or bread, B3 deficiency is very unlikely. The NHS puts the requirement at about 16.5mg a day for men and 13.2mg for women and says you should be able to get all of it from your diet. Your body can also make niacin from the amino acid tryptophan, so pellagra comes from a shortfall of niacin and/or tryptophan, not niacin alone.
The people who do get it share a short list of causes:
- Chronic heavy drinking. The Krak�w review names it, alongside certain medications, as where pellagra turns up today. Heavy drinkers often run low on thiamine (B1) too, and 26% of the Bangalore pellagra patients also had Wernicke's encephalopathy.
- Isoniazid, the tuberculosis drug. A 2021 review from Dundee and Malawi links wider isoniazid prophylaxis to more pellagra cases.
- Carcinoid tumours, which pull tryptophan into making serotonin and leave less for niacin. A 2026 case report describes pellagra from tryptophan depletion in carcinoid syndrome.
- Eating disorders and very restricted diets. Pellagra has been reported as a rare complication of anorexia nervosa.
Riboflavin also plays a part. Riboflavin deficiency can cause a secondary niacin deficiency, because B2 is needed to turn tryptophan into niacin. Our B2 explainer covers that link.
What to do if the signs fit
See a doctor, and say "pellagra" out loud. Diagnosis is mostly clinical, with lab tests in a supporting role, and the treatment is cheap. The Boston authors recommend oral nicotinamide, 100mg three times daily for 3 to 4 weeks, started before lab confirmation. In the Bangalore group, every patient's pellagra symptoms resolved within three weeks of inpatient treatment.
That is a medical dose for a medical problem. Don't self-treat a rash plus confusion with something from the supplement aisle.
For everyone else, the job is boring. Eat protein, which brings both niacin and tryptophan. Keep drinking within sensible limits. If you take a supplement, check the form. The NHS warns that high doses of nicotinic acid can cause skin flushes, and its safe-intake figures for the two forms are very different. The NHS quotes the Department of Health and Social Care as saying 17mg or less of nicotinic acid, or 500mg or less of nicotinamide, a day is unlikely to cause harm.
The point
Pellagra is rare where food is plentiful, but it hasn't gone anywhere. It just moved to people whose drinking, medication or diet quietly cuts them off from niacin, and it hides behind withdrawal or a bad sunburn until someone thinks to ask.
Fireblood contains vitamin B3 as niacinamide, 31mg NE per scoop, alongside 38 other ingredients including riboflavin 5-phosphate. It covers the daily baseline, and you can pick a plan here. It is not a treatment for pellagra, and if the signs above fit, that conversation belongs with your doctor. See the full formula here.
