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.

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."