Obama Dog Sunny Bites White House Guest

President Obama had to deal with a small domestic crisis at the White House -- a family friend was bitten by Sunny, the First Family's 4-year-old dog.

We're told the incident occurred Monday when the 18-year-old was visiting the White House. Sources connected to the girl tell us she went to pet and kiss Sunny, and the dog bit her on the face.

Sunny -- a female Portuguese Water Dog -- left a nasty gash under the girl's eye. We're told the Obamas' family physician, Dr. Ronny Jackson, checked her out and decided she needed stitches.

She's gonna be okay, but we're told she'll likely have a small scar ... which upset her. She posted various pics of the injury and her visit to Dr. Jackson on social media.

The bite is out of character for the breed, which typically is not aggressive in family situations. The Obamas have 2 Portuguese Water Dogs -- 8-year-old Bo has the title,"First Dog."

We reached out to the White House. No comment on the incident.