Diabetes can be hard to manage, but not properly controlling the disease can have dangerous and potentially deadly consequences. Ketoacidosis is one of them.

This condition happens in people who don’t have enough insulin in their body, perhaps because they have not taken some of their insulin shots. The U.S. National Library of Medicine explains that when insulin is lacking, and the body cannot use ingested sugar as a fuel source, it starts to break down fat, which releases acids called ketones into the bloodstream.

In large numbers, those ketones are poisonous and can cause deep, rapid breathing, dry skin and mouth, frequent thirst, a flushed face, headache, nausea, stomach pain, muscle stiffness, muscle aches, frequent urination, difficulty concentrating and fruity-smelling breath. If left untreated, the condition can be fatal, in part because it can eventually cause fluid to build up in the brain and for the heart and kidneys to stop working.

There are ways to tell whether you have the condition or are approaching it, the Mayo Clinic says. A routine blood sugar test like the kind diabetics take all the time will show high blood sugar, and there are tests to measure the ketone levels in urine. The American Diabetes Association says that experts usually recommend using a urine test strip to check for ketones when blood glucose levels reach higher than 240 milligrams per deciliter. And when sick with a cold or flu, a person should “check for ketones every four to six hours” to be safe. That’s because infections or other illnesses can increase hormones like adrenaline and cortisol in the body, which then counter the work of insulin — “pneumonia and urinary tract infections are common culprits,” the Mayo Clinic warns.

In addition to missed insulin shots and illness, stress, a heart attack, alcohol or drug abuse could also trigger ketoacidosis.

However, some people who are at risk of developing ketoacidosis do not even know to look out for it: Diabetic ketoacidosis “is sometimes the first sign of type 1 diabetes in people who have not yet been diagnosed,” the library of medicine says.

For those who know they are at risk for the condition, there are measures that can prevent ketoacidosis. The Mayo Clinic lists eating healthy and exercising, closely following your insulin or medication regimen and monitoring blood sugar and ketone levels regularly. “Diabetes complications are scary,” the organization says. “But don't let fear keep you from taking good care of yourself. Follow your diabetes treatment plan carefully, and ask your diabetes treatment team for help when you need it.”

The American Diabetes Association also warns against exercising when tests show high blood sugar or ketone levels, and to instead check in with a doctor.

Once ketoacidosis arrives, it can be treated. The Mayo Clinic says fluids, electrolytes like sodium and potassium, and insulin are all used to relieve the condition.