A 20-year-old man’s switch to the keto diet dramatically changed his body—just not in the way anyone would have expected.
Doctors writing in this week’s New England Journal of Medicine detailed how the man developed a rare skin condition often caused by switching to keto, one that covered his neck and chest in itchy rashes. Despite the alarming symptoms, the condition is readily treatable, provided the person can be convinced to stop their diet.
Keto rash
This latest case was presented as a part of a regular segment in the NEJM detailing unusual or noteworthy medical images.
According to the report, the otherwise healthy man visited a dermatology clinic four weeks after developing a peculiar rash. He told doctors that two months earlier, he had started a keto diet for weight loss.
The skin condition is formally called prurigo pigmentosa, though it’s better known by its nickname, “keto rash.”
Scientists aren’t really sure why the condition occurs, but it’s strongly linked to someone entering ketosis, a metabolic state in which the body breaks down stored fat as its primary source of energy instead of glucose. Keto diets induce ketosis by heavily limiting carbohydrate-rich foods, though other health conditions can trigger it as well.
The rash develops across several phases. It usually begins as small, itchy red or purple bumps along the neck, chest, and back. These bumps then enlarge and form a distinctive net-like (reticular) pattern on the skin; they can sometimes fill with fluid and crust over, similar to blisters. The bumps may become less itchy and fade over time but can recur repeatedly, eventually leaving behind persistent darkened (hyperpigmented) spots.
Rare and resolvable
All this said, keto rash remains an incredibly rare complication of ketosis.
According to a 2019 paper, only around 300 cases had been documented worldwide at the time, including just 20 cases in the U.S. The condition has been most commonly reported among women of East Asian ancestry, particularly in Japan, but not exclusively, as with this latest report.
Rare as the rash is, its incidence could be rising with the increased popularity of keto diets. And because it’s seldom seen, doctors may mistake the rash for more common skin conditions like eczema. Once identified, however, it can be easily treated.
The rash eventually goes away once a person leaves ketosis, though it might take a few weeks to clear. For most cases, that means ending the keto diet (cases not linked to a keto diet tend to go away on their own). Tetracycline antibiotics are commonly used to manage its symptoms, since they have anti-inflammatory effects. As for our protagonist, the report authors didn’t detail whether the man took their advice and ditched the keto diet.
Strange rashes aren’t the only weird side effect of trendy diets. Last January, doctors described how a man’s high-fat “carnivore” diet full of cheese, butter, and meat caused his hands to literally seep out cholesterol.