Got a rash when you started keto? Or are you worried about getting one and not sure how to prevent it? Take a look at five things you ought to know, starting with...
1. What is keto rash?
The technical name for keto rash is prurigo pigmentosa, but call it PP for short. PP is a type of inflammatory skin disease. It causes red bumps, typically on the neck, chest, and back - sometime, the bumps fuse together into a bigger raised red area called a plaque. And it’s itchy. As this study put it, “At the outset, lesions are intensely pruritic and signs of excoriation are common.” To translate from science to English, it’s so itchy that patients show up with wounds from scratching themselves so hard they break the skin. Not fun!
For the sake of people who get freaked out by this type of thing, we haven’t included any actual pictures of PP in the article, but if you’re curious and not bothered by looking at people’s horrible rashes, you can easily image search and come up with hundreds.
Keto is actually just one potential cause of PP, and despite the nickname “keto rash,” you don’t even necessarily have to be a ketogenic diet to get it. Anything that causes an elevation in ketone level seems to be able to trigger PP. This obviously applies to people on ketogenic diets, but it also covers people who do a lot of fasting and people with uncontrolled Type 1 Diabetes.
Some case reports have also found PP in patients who just lost too much weight, too fast. In this case study, a woman got it after dieting so hard she became dangerously underweight and developed “trace ketosis” (basically she was dieting so much that she was borderline fasting, so her ketone levels went up). Here, a teenaged girl got PP after losing 20 kilograms (44 lbs) in 3 months on an ultra-strict diet.
These cases are relevant to keto dieters because people eating keto often do lose a lot of weight quickly. It’s not always easy to figure out what’s to blame for various symptoms and side effects: the keto diet or the rapid weight loss.
2. How can a keto diet cause a rash?
First of all, it doesn't cause a rash in most people. Keto rash is still pretty rare, although anecdotally getting more common with more and more people following a keto diet. A lot of people eat keto for years without ever getting a rash at all.
As for what happens with the unlucky folk, nobody really knows. There’s a bunch of research finding that starting keto can bring on the rash and quitting keto can stop it, but the “how” is incredibly vague. This study takes a stab at it:
“Ketone bodies are thought to accumulate around blood vessels, leading to a predominantly neutrophilic inflammation. The ketones subsequently enter the cells, leading to alterations in intracytoplasmic cellular processes.” [note: "intracytoplasmic" = inside the cytoplasm, which is part of the inside of a cell]
That’s kind of interesting, but doesn’t explain why the vast majority of people who try keto never get a rash. What make some people so much more susceptible? The paper suggests that it may have something to do with interactions between diet and the gut biome, but for now it’s kind of a mystery still.
3. How is keto rash/prurigo pigmentosa different from other types of rashes?
Keto rash/PP is not:
- A food allergy. While the problem is diet related, there’s no evidence that keto rash has any relation to a specific allergic response to a particular food.
- "Detox.” It’s true that you do store toxins in your fat tissue, and as you lose weight your body flushes them out. But if prurigo pigmentosa came from weight loss detox, it would happen with all diets that successfully cause weight loss, and it would be more likely with extreme weight loss. That’s clearly not the case - not all people who lose huge amounts of weight get a rash - so this can’t be the answer.
It’s not always easy to visually see the difference between PP and other types of skin reactions - this study for example, noted that many patients with PP had mistakenly been diagnosed with eczema - which is why you should always see a doctor for mysterious skin conditions.
4. Does it go away on its own?
Sometimes - this case series reports a woman with PP who tried cortisone with no luck but eventually found that the problem fixed itself after 10 weeks. But that’s a long time to live with an itchy rash!
PP can also come and go. It doesn’t necessarily disappear and then stay out of your life forever: One analysis of multiple cases found that with no treatment, symptoms can come and go for up to 7 years.
As a parting gift, PP is also known for leaving darker areas on the skin for months or even years after the actual itchy rash has gone away - not dangerous, but very annoying.
5. What can I do to fix it?
Well, you could eat more carbs, if keto is more of an experiment in optimization than a lifestyle commitment. It’s not actually necessary to go super high-carb - a standard low-carb but not-quite-keto diet might be fine. To illustrate, this article gives two very interesting case studies (it also has a lot of very clear photos of the rashes):
Case 1: a 43-year-old woman who started keto to lose weight. She tried eliminating nuts, changing shampoo brands, and applying topical steroids to reduce inflammation: none of it helped. She went back on a higher-carb diet and the rash went away.
Case 2: an 18-year-old man who started keto to control his seizures. Seizure control was obviously critical for him, so he couldn’t just go off the diet. He got the rash on day 9, and by day 14 it was really bad. He upped his carbs from 16 to 51 grams per day, then to 90 grams per day. This reduced his urinary ketone count and resolved the rash. But the patient didn’t have to completely go out of ketosis - he just had to induce a slight reduction in ketones. The authors suggested that this could be an option for people who don’t want to completely abandon ketosis - incrementally add carbs and see if you can reduce total ketone production without getting out of ketosis completely.
In the case of strict dieting, the researchers in the case studies simply re-fed the people. For example, remember the severely malnourished dieting woman from above? The case study reported that her rash resolved after she started eating enough food again.
Failing that, other studies note that antibiotics have also been used to treat PP in adults, but that’s a job for a doctor.
Keto rash: don’t let it wreck your keto experience!
Keto rash isn’t super common, but it’s definitely a thing that exists - you’re not going crazy. If you get a rash right after starting keto, it’s definitely worth checking out.