January Jones has posted a topless selfie to promote Breast Cancer Awareness Month.

The 40-year-old actress is encouraging women to check their boobs for lumps and to see a doctor if they have concerns about their mammaries and along with her bold photo she gave her 634,000 Instagram followers advice on where to get a free mammogram in Los Angeles.

The 'Mad Men' star shared a playful bathroom selfie on the social media platform showing herself grinning in the mirror covering her breasts with just her arm, with a Halloween inspired filter on her face.

She wrote: ''It's breast cancer awareness month gals and guys! This is a friendly reminder to get a mammogram! @tamaramellon is offering FREE mammograms regardless of insurance status next wk in a mobile RV in Los Angeles! Oct 8, 9, 10th! Sign up at link in bio! #LoveYourMellons (sic)''

January was flooded with comments of support from fans who encouraged early detection.

One user said: ''Self-breast exam monthly, ladies! Early detection is best, but please get squished once a year, too! (sic)''

Another wrote: ''Good call! When in doubt, check em out. Early diagnosis! (sic)''

January isn't the only star getting involved in Breast Cancer Awareness Month.

Serena Williams posed topless in a music video last month to encourage fans to touch themselves for a good cause.

The 37-year-old tennis champion sang a cover of 1990 Divinyls hit 'I Touch Myself' in a bid to get women to examine their breasts.

The sports star shared the video on her Instagram and wrote: ''This Breast Cancer Awareness Month I've recorded a version of The Divinyls global hit 'I Touch Myself' to remind women to self-check regularly.

''Yes, this put me out of my comfort zone, but I wanted to do it because it's an issue that affects all women of all colors, all around the world. Early detection is key - it saves so many lives. I just hope this helps to remind women of that.''