TikToker Taylor Rousseau Grigg died at just 25 years old from complications of Addison’s disease and asthma, her family told Today.com. Rousseau Grigg’s death last week was “sudden and unexpected,” her husband, Cameron Grigg, said in an Oct. 5 Instagram post.

The young TikToker had become famous by posting messages about her life. She said she had been diagnosed in an August 8 “health update” but did not specify her condition. Experts say Addison’s disease is rare, but can quickly become life-threatening if not treated properly.

Here’s what you need to know about the condition.

What is Addison’s disease?

Addison’s disease is an autoimmune disease (affecting about one in 100,000 people) in which the body attacks its organs, especially the adrenal glands. It is also called primary adrenal insufficiency because the condition causes a person’s adrenal glands to produce too little of two important hormones. “The most important thing is the hormone cortisol – you can’t survive without cortisol,” says Dr. Anne Cappola, an endocrinologist at Penn Medicine, told Yahoo Life.

Cortisol is often called the “stress hormone,” and its levels rise as part of the “fight or flight” response when we are in real danger or otherwise distressed. But it plays a crucial role in our body. “Cortisol is an important hormone for blood pressure, so if you don’t have enough of it, you can go into adrenal crisis and die,” explains Cappola. But, she adds, the body has a lot of “redundancy” when it comes to cortisol. We have two adrenal glands – as well as other cells – that produce cortisol, and in most cases we could get by on the amount of the hormone produced by one. That’s why the symptoms of Addison’s disease can develop slowly over time.

What are the symptoms?

Addison’s disease manifests with a “constellation” of symptoms, says Dr. Theodore Friedman, an endocrinologist and chairman of the department of internal medicine at Charles R. Drew University, told Yahoo Life. These include fatigue, weight loss, nausea, diarrhea, abdominal pain, joint or muscle pain, dehydration, low blood sugar and cravings for salty foods. It can also cause hyperpigmentation, or a darkening of the skin that can make people look bronzed.

Rousseau Griggs said in her August health update that she sometimes “writhed in bed in pain” and felt too weak to carry a suitcase or walk to the mailbox. She added that she had only discovered what was wrong with her a few months earlier and that she “struggled all the time with the feeling that I was going to die.”

Although symptoms develop slowly over time, in some cases they can worsen quickly, Friedman says. “You can be healthy one day and sick the next,” he explains. “It can happen very quickly.” According to the Cleveland Clinic, most people are diagnosed between the ages of 20 and 50 as the chronic effects of the condition build up.

Addison’s disease is treatable with steroids

Cappola and Friedman tell Yahoo Life that people with Addison’s disease usually need to take one or two medications to replace the hormones their bodies are producing too little: hydrocortisone, a steroid that replenishes cortisol, and fludrocortisone, to replace a second hormone that is called aldosterone. The latter helps balance the body’s water and salt levels, says the Cleveland Clinic, so people with Addison’s may need to consume more sodium when exercising.

If you use these steroids properly — hydrocortisone sometimes needs to be taken in varying doses, between two and four times a day, Friedman says — an Addison’s patient can live a relatively normal life.

How Addison’s can become fatal

The disease must be managed carefully. The body needs cortisol at all times, “but you especially need cortisol during times of physical stress,” Cappola explains. The body’s cortisol needs can fluctuate dramatically throughout the day and “increase during times of stress, such as during an infection.”

This is especially dangerous when a patient’s body is trying to fight off a cold or other illness. “An infection causes you to chew through (your steroids), after which you can no longer fight the infection,” Friedman explains. People with Addison’s disease need an extra dose of cortisol during these times, often in injection form, because their body cannot produce enough to meet the demand itself.

The biggest concern, however, is that the drop in cortisol causes an adrenal crisis, and if there is not enough of the hormone, “the main thing you see is that blood pressure starts to drop, and if your blood pressure drops If the temperature is not high for a long time enough, it can kill you,” says Cappola.

While it’s not clear what exactly happened to Rousseau Grigg, both experts say a combination of Addison’s adrenal crisis and asthma could be fatal. “It may not be the asthma attack itself,” says Cappola. ‘But she may have had an upper respiratory infection that caused an asthma attack and adrenal crisis. Both can kill you.”

Cappola points out that a new diagnosis could mean that Rousseau Griggs was less willing to understand what was happening or how to deal with it. She adds that the drop in blood pressure during an adrenal crisis may have impaired judgment and made it more difficult to get help or more medication in time.

Both experts say that unless a patient has had persistent symptoms (which would warrant a doctor’s visit), Addison’s is a rare diagnosis that most people probably don’t need to worry about. “What should be reassured is that the body has a lot of built-in duplication of adrenal gland tissue that makes these hormones,” says Cappola. “It really takes a chronic destructive process to get to the point where someone develops these symptoms.”

Although corticosteroids such as hydrocortisone and prednisone are helpful for people with Addison’s disease, Cappola cautions people against taking the medications without a doctor’s recommendation. “Be careful using corticosteroids such as hydrocortisone or prednisone,” Cappola warns. “There are people who think they have adrenal fatigue and take these (as) supplements, and they shouldn’t; you don’t want to mess with those adrenal glands.” That’s because if you take steroids for a long time and stop abruptly, your body can go into adrenal crisis, even if you don’t have Addison’s.