High severity

Poll evil (Nuchal bursitis)

Poll evil is inflammation or infection of the nuchal bursa at the poll (behind the ears / occiput) — it can drain through fistulous tracts. It is not fistulous withers (supraspinous bursa at the withers — a different place), not sweeney (shoulder muscle atrophy / suprascapular nerve), and not strangles (lymph nodes / respiratory). A photograph cannot diagnose poll evil. A still cannot tell poll evil from a poll abscess, trauma swelling at the poll, an insect bite/swelling, or fistulous withers (withers is a different place). Diagnosis is a vet exam. The skin scan is a first look at the poll skin/swelling to share with a vet, not a poll-evil test, and there is no poll-evil scanner.

Symptoms to watch for

Swelling, heat, or pain at the poll — the swell is a clue, not a still-photo verdict

Draining tracts or discharge at the poll after hitting the head or a poorly fitting bridle/halter

A poll swelling that can look like a poll abscess, trauma swelling, an insect bite/swelling, or fistulous withers — a still cannot tell them apart (withers is a different place)

Heat or a draining opening at the poll — a reason to book a vet, not a photo verdict

Pain at the poll after bridle, halter, or head trauma — location is a clue, not a diagnosis

Some horses show only swelling at the poll at first; draining tracts can come later — that is a vet visit, not a photograph

Common causes

Inflammation or infection of the nuchal bursa at the poll (behind the ears / occiput), which can drain through fistulous tracts
Trauma at the poll from hitting the head or a poorly fitting bridle/halter — the history is a clue, not a diagnosis
Not fistulous withers (supraspinous bursa at the withers — a different place), not sweeney (shoulder muscle atrophy / suprascapular nerve), and not strangles (lymph nodes / respiratory)
Not a poll abscess, not ordinary trauma swelling at the poll, and not an insect bite/swelling — a still cannot tell poll evil from those, and those need a vet

Prevention

Fit the bridle and halter so they do not pinch, rub, or bruise the poll
Watch the poll for new swelling, heat, pain, or a draining tract and rest rather than riding through it
Protect the poll from trauma in work and in the stall — hitting the head is a common history, not a photo verdict
Do not treat a photo, a poll swell, or a scan result as a diagnosis
Skin photos can help you and the vet look at the poll skin and swelling — they do not confirm or rule out poll evil, and they cannot tell it from a poll abscess, trauma swelling, an insect bite/swelling, or fistulous withers

What to do

1
Book a vet visit if the poll is swollen, hot, painful, or draining. Diagnosis is a vet exam — not a photograph.
2
Stop riding through a painful or draining poll. Rest the horse and do not add a tighter bridle or extra work hoping the swell will go down.
3
Photograph the poll in good light, from the side and from above, and keep the photos on the horse's record so you and the vet can see change over time — a first look to share, not a diagnosis.
4
Use a skin scan only as a first look at the poll skin/swelling to share, not as a poll-evil test. There is no poll-evil scanner.
5
If poll evil (nuchal bursitis) is confirmed, follow the plan your vet prescribes. Do not start a treatment protocol from a photo.
6
Keep the vet on the same page. Share what you see; do not treat a photo as a verdict.

When to call the vet

Pick up the phone if…

Schedule a vet visit if the poll is swollen, hot, painful, or draining, or if the swell appeared after hitting the head or a poorly fitting bridle/halter. Call sooner if the horse is dull, off feed, in obvious pain, or if you are worried about Brucella — that is a vet call (zoonotic), not a photo diagnosis. A photograph cannot diagnose poll evil. A still cannot tell poll evil from a poll abscess, trauma swelling at the poll, an insect bite/swelling, or fistulous withers (withers is a different place). Diagnosis is a vet exam. The skin scan is a first look at the poll skin/swelling, not a poll-evil test, and there is no poll-evil scanner.

Get a first look at the poll skin

Scan the skin in HorseCare. 5 free scans this month, then Pro.

Scan the skin

5 free scans this month, then Pro. Scans run in the HorseCare app.

Educational content only. Not a substitute for veterinary advice.