Selena Gomez has been treated for lupus but what is it?
Selena Gomez has revealed she took a break from music after being diagnosed with lupus.
The 23-year-old says she's had chemotherapy to treat the disease affecting the body's immune system. But what exactly is lupus?
According to the NHS, lupus is a complex and poorly understood condition that affects many different parts of the body.
Its symptoms range from mild to life-threatening.
There are some types that just affect skin, but the term is usually used to describe a more severe form of the condition - lupus erythematosus (SLE).
That affects many parts of the body, including the skin, joints and internal organs.
Signs and symptoms
Lots of people can have the condition for a long time without knowing before they get a sudden flare-up.
The symptoms include extreme tiredness, rashes (especially on the face, wrists and hands) and joint pain and swelling.
Even mild cases can be distressing and have a big impact on quality of life.
But the symptoms can be similar to more common conditions so it's often hard to diagnose.
SLE can put some people at greater risk of complications like infections, heart attacks or strokes.
Steph Tovey, who's 23, started getting symptoms around April 2011. She hadn't heard of the condition until she was diagnosed and had to take three months off work.
"I was really very unwell, I was on a lot of medications. Now day to day [it's] not so bad but I do still suffer. I get little aches and pains," she says.
"The fatigue is the biggest issue, no matter how much you rest, you don't feel better for it."
She says it's a massive deal that Selena has publicly announced her illness and says it must be really hard for her.
"It's is quite an unknown condition so the awareness that is raised is a massive deal to those of us who suffer from it."
"Sometimes you don't even want to get out of bed, let alone touring round and standing on stage, that would be a lot of energy that some days you really don't have."
Meanwhile, Rachel Warburton has told Newsbeat doctors thought it was a cold when she first got the symptoms.
"My joints started flaring up so I got really swollen joints a lot of pain. I couldn't even stand up.
"It has affected my day-to-day life in that I to have to take care of myself, there's things I can't do. I have to cancel plans quite a lot if I'm sick."
She's also got a lot of understanding for Selena's situation.
"Sometimes I can't get out of bed, let alone have a camera in my face every five minutes".
What causes lupus?
In the most sever form of lupus, the immune system starts to attack and inflame healthy cells, tissue and organs.
It's not known why it happens but it's thought it's often down to a combination of genetic and environmental factors.
It's a rare condition and is thought to affect around 15,000 people in England and Wales.
Around 90% of those affected are women and it's most common in those between 15 and 50.
It's more common in people of African, Caribbean or Asian ethnicity.
How do you treat it?
At the moment there's no cure for SLE but treatments have got much better, with drugs to help with the symptoms and reduce the risk of organ damage.
Chemotherapy can sometimes be used to suppress the immune system - that's a mixture of drugs.
A few decades ago SLE was seen as a terminal condition, with many people dying from complications within a few years of diagnosis.