Red lump on chicken

[cat101]

Hello, I'm wondering if someone can help me. A couple months ago I rescued a few hens from BHWT however one had a red lump the size of a 10p almost at the base of her back, which was featherless. The lump appears to have grown in the couple months I've had her and the redness has spread all the way down her side and there is no sign of feathers growing through her skin in this area. I'm wondering if anyone has any experience of this before I take her to a vet (she's really timid compared to the other chickens so don't want to stress her out with a vet visit if it's just something simple). She's still eating and drinking normally and it doesn't appear to bother her, I'm just concerned as it's definitely getting worse. I've attached a picture but it's not the best as she kept running off every time I lifted my phone to take a picture!

 

[junebuggena]

That's the preening gland, and it could be seriously impacted or infected.

 

[cat101]

Thank you for your help, I didn't know such thing existed. I just Googled it and I'm guessing it's too far gone to be cleaned with simply warm water as one site suggested. I will call up the vet tomorrow to get an appointment for her. Thank you very much for diagnosing