“Keto rash” is the informal name for prurigo pigmentosa, a rare, itchy skin rash linked with ketosis. It usually appears as red, itchy bumps on the chest, back and neck that join into a net-like pattern and can leave brown marks as they heal. DermNet, a dermatology resource, describes it as a rare inflammatory skin condition associated with ketosis, from diets, fasting, diabetes or after weight loss surgery. It often improves when you reintroduce some carbohydrate, and doctors can treat it. Keto can also bring other skin changes, from dry skin to changes in acne. If you develop a rash, see a doctor or pharmacist rather than guessing.
What does keto rash look like?
- Red, raised, itchy bumps (papules), sometimes with small blisters.
- On the chest, back, neck and sometimes the armpits, often symmetrically.
- A net-like (reticulate) pattern as the bumps join together.
- Brown or gray marks (hyperpigmentation) left behind as it fades, which can last for weeks or months.
It typically appears days to weeks after starting a very low-carb diet, fasting, or losing weight quickly.
Who gets it?
Prurigo pigmentosa is rare. A systematic review of 369 reported cases from 24 countries found that most patients were young, with a mean age of about 26, and about 72% were female. Dietary changes were the most commonly reported trigger, and among those cases, about 40% had started a ketogenic diet. Friction from clothing and sweating were also reported as aggravating factors. Most early reports came from East Asia, but people of all backgrounds can be affected.
Why does it happen?
The exact cause isn’t known. It seems to be linked to ketone bodies in the blood, which may trigger inflammation around blood vessels and hair follicles in the skin in susceptible people. Friction, heat and sweat may make it worse.
How is it treated?
See a doctor or dermatologist if you develop a rash on keto, as several skin conditions can look similar, including eczema, contact dermatitis and fungal infections. If it’s prurigo pigmentosa, options may include:
- Reintroducing carbohydrates. Many cases improve after people eat more carbs and leave ketosis.
- Prescription anti-inflammatory antibiotics, such as doxycycline or minocycline, which are commonly reported as effective.
- Soothing measures: loose cotton clothing, avoiding friction and overheating, and gentle, fragrance-free moisturizers.
Don’t try to treat a rash with supplements or by stopping prescribed medicines. If the rash spreads quickly, blisters badly, or you feel unwell with a fever, get medical help promptly.
Other skin changes on keto
Dry skin
The fluid and salt losses of early keto can leave skin feeling dry. Drinking enough water and using a moisturizer usually helps. Our guide to keto electrolytes explains how to stay balanced.
Acne changes
Some people find their acne improves when they cut sugary and high-glycemic foods, while others notice breakouts, possibly from more dairy or hormonal changes during rapid weight loss. The American Academy of Dermatology says a low-glycemic diet may lead to fewer pimples, based on small studies. Our guide to foods for healthy skin covers the evidence.
Hair shedding
Temporary hair shedding can occur a few months after starting any diet that causes rapid weight loss. It’s usually linked to eating too few calories or too little protein. Our guide to nutrient deficiencies on keto explains which nutrients matter.
Body odor and breath
Ketones can cause a fruity or metallic smell on the breath, sometimes called “keto breath.” It usually fades as your body adapts. Drinking water and good oral hygiene help.
How to reduce your risk
- Ease into keto by lowering carbs over a week or two rather than overnight.
- Stay hydrated and keep electrolytes in balance.
- Wear loose, breathable clothing and avoid heavy sweating against the skin if you’ve had the rash before.
- Don’t aim for very high ketone levels. For weight loss, you don’t need deep ketosis.
- Stop and seek advice if a rash appears.
When to see a doctor urgently
Most rashes on keto aren’t serious, but get medical help quickly if:
- The rash spreads very fast or covers a large area.
- You have blistering, peeling skin or sores in your mouth.
- You feel unwell, with a fever or swollen glands.
- You’ve started a new medicine recently, which can cause drug rashes.
- You have diabetes and feel very unwell, are vomiting or breathing fast, which can be signs of ketoacidosis.
People with type 1 diabetes, or type 2 diabetes treated with certain medicines, should be especially careful with very low-carb diets, as dangerously high ketone levels can develop. The NHS explains the warning signs of diabetic ketoacidosis. Our article on keto and type 2 diabetes covers the risks.
Looking after your skin on keto
- Moisturize daily with a fragrance-free product, especially in the first weeks.
- Shower after sweaty exercise and change out of damp clothes.
- Eat plenty of vegetables, nuts, seeds and oily fish for vitamins, minerals and healthy fats.
- Use sun protection, as you would on any diet.
Common questions
Can keto rash come back?
Yes. Some people find it returns if they go back into deep ketosis. If you’ve had it once, a less strict low-carb diet may suit you better.
How long does keto rash last?
The itchy bumps often settle within days to weeks once treated or after reintroducing carbs, but the brown marks can take months to fade.
Can I stay on keto if I get keto rash?
Some people can, with treatment from a doctor. Others find that eating a little more carbohydrate, enough to leave strict ketosis, is the simplest solution. Discuss it with your doctor.
Is keto rash dangerous?
It isn’t usually dangerous, but it can be very itchy and distressing, and it’s easily confused with other conditions, so get it checked.
Safety note: Keto isn’t suitable for everyone. If you have diabetes, kidney or liver disease, take regular medication, or are pregnant or breastfeeding, talk to your doctor before cutting carbs this far (why it matters).
This article is general information, not medical advice. Talk to your doctor or a registered dietitian before making big changes to how you eat, especially if you have a health condition, take regular medication, or are pregnant or breastfeeding.
