what could cause a bruise below my collarbone after endoscopy?

Hi.

Firstly, the bruise and red mark you noticed after your endoscopy are likely related to the procedure itself. Endoscopies are generally safe, but they can sometimes result in minor bruising or skin marks, especially in sensitive areas like the neck and chest. Here are a few possible explanations:

Pressure or Contact: During an endoscopy, various instruments and equipment are used, and sometimes external pressure is applied to facilitate the procedure. This pressure or contact, even if gentle, can sometimes cause bruising or red marks on the skin, particularly in areas where the skin is thin or sensitive.
Reaction to Adhesive or Disinfectant: If any adhesive was applied to your skin or a disinfectant was used during the procedure, you might see a temporary mark. This is especially true if you have sensitive skin or a mild allergic reaction to these substances.
Vascular Reaction: Sometimes, the body can have a mild vascular reaction to the procedure, which could manifest as a red mark. This is usually harmless and resolves on its own.
Non-Removable Stain: If the red mark doesn't wash off and isn't raised or painful, it might be a non-removable stain from something used during the procedure, such as an antiseptic solution.

Since you mentioned that the red mark does not wash off, it's likely not blood but could be one of the other causes mentioned above. However, it's always good to monitor the area. If you notice any changes, like the area becoming swollen, painful, or showing signs of infection, it's advisable to seek medical attention sooner rather than waiting for your follow-up appointment.

In the meantime, keeping the area clean and avoiding irritation can help. If the bruise is bothersome, applying a cold compress in the first 24-48 hours can reduce swelling, followed by a warm compress to help dissipate the bruise.