Photo: Madonna shows off long armpit hair on Instagram

Madonna is letting it all hang out -- at least when it comes to her armpit hair.

The 55-year-old pop star posted a photo on Instagram Thursday showing off long underarm hair, along with the caption: "Long hair...... Don't Care!!!!!! #artforfreedom #rebelheart #revolutionoflove."

One of Madonna's hashtags coincides with Art For Freedom, a global initiative -- led by the singer and VICE -- that encourages creative expression with hopes of bringing awareness to human rights violations. Fans are encouraged to contribute art works that promote freedom of speech.

Underarm hair

Is it OK for women to let their armpit hair grow long?

Madonna isn't a stranger to letting her underarm hair grow, by the way. In 2011, she told Harper's Bazaar, "Going to high school, I saw how popular girls had to behave to get the boys. I knew I couldn't fit into that. So I decided to do the opposite. I refused to wear makeup, to have a hairstyle. I refused to shave. I had hairy armpits."