What is Alopecia? Here's what you should know about the condition as popular TV presenter Louis Theroux shares an update with fans.

The 'Weird Weekends' star, 53, posted an Instagram snap to update fans on Tuesday evening because he was worried that he'll "freak everyone out".

The documentary film-maker first addressed his Alopecia barbae ("of the beard") in June where he shared that "nature [had]played a cruel trick on {him]" alongside a picture of his beard that showed a "tiny remnant" missing.

Louis Theroux joked with fans that he can "now only grow a weird little Hitler moustache".

What is Alopecia?

The disease Alopecia occurs when the body's immune system starts to attack hair follicles which in turn causes hair loss to begin in patches, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases. 

Hair can be lost from any part of the body but the condition often affects the head and face.

While the disease isn't considered a serious medical condition, it can cause anxiety for those suffering from it.

The condition can have a number of causes such as age, genetics and stress.

Alopecia can be caused or worsened by stress with this being one of the most commonly sighted causes.

Alopecia symptoms 

As mentioned above, Alopecia Areata primarily affects hair but can see changes to nails as well.

The National Institutes of Health body explained that "Alopecia areata typically begins with sudden loss of round or oval patches of hair on the scalp."

However, the beard area in men, or the eyebrows or eyelashes are among the other areas that could be affected.

It added: "There is usually no sign of a rash, redness, or scarring on the bare patches.

"Some people say they feel tingling, burning, or itching on patches of skin right before the hair falls out."

Meanwhile, some nail changes include ridges and pits.

For more information, advice and support, visit the National Institute of Arthritis and Musculoskeletal and Skin Diseases website.

Louis Theroux issues Alopecia update as condition spreads

In the update on Tuesday, Theroux shared: "Oh jeez it looks like the alopecia has migrated up to my eyebrow.

"I realise you aren’t all awaiting every update on its progress but I want people to acclimatise to the new partially depilated me and not freak everyone out by suddenly appearing in public like a half-plucked elephant bird with no forewarning.

"So this is where we’re at. I’d really like to keep my eyebrows, but it’s out of my hands at this point… tho I have started taking vitamin d and something called biotin."