A weird, itchy rash is linked to the keto diet—but no one knows why

negative aspects of diet

Otherwise, the keto diet is popular among people who are trying to lose weight, especially those who are trying to lose visceral fat, as explained in the case study. Anecdotal reports promote the keto diet as being effective in helping people slim down relatively quickly, as well as improving stamina and mental clarity. But strong clinical data supporting these claims is lacking, and medical experts have raised concerns about long-term heart health, among other things.

The diet also has obvious disadvantages. Ketones are acidic, and if they accumulate too much in the blood, they can be toxic, causing ketoacidosis. This is a particular concern for people with type 1 diabetes and those with chronic alcohol abuse. For everyone else, there is a list of common side effects, including nausea, vomiting, constipation, diarrhea, bad breath, headache, fatigue, and dizziness. The ketogenic diet is also linked to high cholesterol and kidney stones.

But there is one side effect that is well established but little known and still puzzling to doctors: “keto rash” or prurigo pigmentosa. This rash exactly fits the man’s case – a red, raised, itchy rash on the neck, chest and back, as well as areas of hyperpigmentation, also develop.

This rash was first identified in Japan in 1971, where it was seen mostly in women. Although it has been consistently linked to metabolic disorders and dietary changes, experts still don’t understand what causes it. This is seen not only in people on the keto diet but also in people with diabetes and those who have had bariatric surgery or are fasting.

In a review this month, researchers in Saudi Arabia said a leading hypothesis is that high levels of ketones in the blood cause inflammation around blood vessels driven by a type of white blood cell called neutrophils, and this inflammation itself causes the rash, which develops in different stages.

Although the condition is still poorly understood, at least effective treatments have been worked on. The most common treatment is to take the person out of ketosis and give them an antibiotic of the tetracycline class. Antibiotics are designed to treat bacterial infections (which it is not), but they can also reduce signs of inflammation and thwart the activity of neutrophils.

In that man’s case, doctors gave him a two-week course of doxycycline and told him to go off the keto diet. After a week, the rash was gone.