☀️ Vet Guide: Sunburn vs. Photosensitization in Horses | 2025 Causes, Symptoms & Liver-Linked Skin Reactions 🐴

By Dr Duncan Houston, BVSc

Horses with pink skin and white hair are especially prone to UV-related skin conditions. While **sunburn** is the most common and easily recognized, another condition—**photosensitization**—can appear nearly identical but may indicate a much more serious internal issue. 🧠🐎

In this 2025 guide, I’ll explain how to distinguish between sunburn and photosensitization, what plants or liver problems may cause it, and how to respond when your horse’s skin reacts to the sun. ☀️🧬

☀️ Sunburn in Horses

Sunburn typically affects **areas of thin skin and sparse pigmentation**, such as:

• 👃 The muzzle and nose
• 👀 Around the eyes
• 🦷 The lips and sometimes ears

It’s most common in horses with **white or light-colored coats** and pink skin. Damage is caused by **direct UV light exposure**, especially in summer months or at high altitude. 🌞

Signs of Sunburn:

• 📉 Red or inflamed skin
• 🔥 Pain and sensitivity in affected areas
• 📦 Scabbing or peeling, usually localized

Simple Treatment & Prevention:

• 🧴 Apply **zinc oxide cream** to protect the skin
• 😷 Use **UV-blocking fly masks** and nose nets
• 🏠 Stable or shade horses during peak sun hours

Sunburn is uncomfortable, but usually not life-threatening. ✅

🧪 Photosensitization: A Bigger Concern

If your horse is developing **red, peeling skin on white areas beyond the face**, you may be dealing with **photosensitization**—a more serious condition that can indicate internal disease. ⚠️

Photosensitization occurs when a horse’s body **becomes overly sensitive to UV light**, due to compounds in the bloodstream that react to sunlight and damage the skin. This is typically triggered by: 🧬

Two Types of Photosensitization:

1️⃣ Primary Photosensitization:

• 🪻 Caused by ingesting certain plants that contain **photodynamic compounds**
• 🧪 These substances circulate in the bloodstream and react when exposed to UV light

2️⃣ Secondary (Hepatogenous) Photosensitization:

• 🧬 Triggered by **liver damage** that prevents breakdown of chlorophyll byproducts
• 🌿 The liver fails to eliminate **phylloerythrin**, a compound derived from plant chlorophyll
• 📉 Phylloerythrin accumulates in the blood and reacts to sunlight, damaging white skin

🔍 Symptoms of Photosensitization

• ☀️ Red, peeling, or crusted skin in **non-facial white areas**—shoulders, flanks, legs
• 🔥 Swelling, oozing, or skin sloughing
• 😠 Pain or irritation with sunlight exposure
• 🧪 Signs of liver disease—jaundice, poor appetite, depression

Photosensitization **requires veterinary evaluation**, particularly if internal causes are suspected. 🩺

🌿 Plants That Can Cause Photosensitization

Common offenders include:

• 🚫 St. John’s Wort (Hypericum perforatum)
• 🚫 Buckwheat (Fagopyrum)
• 🚫 Smartweed (Polygonum)
• 🚫 Lantana

Others cause **liver damage** that leads to secondary photosensitization, including:

• 🚫 Ragwort and other pyrrolizidine alkaloid plants
• 🚫 Groundsel
• 🚫 Tansy

🩺 Diagnostic & Treatment Strategy

Suspect photosensitization? Don’t guess—get a full veterinary workup. This typically includes:

• 🧪 Bloodwork to evaluate liver enzymes and protein levels
• 🔬 Possible liver ultrasound or biopsy in severe cases
• 🌱 Review of pasture, hay, and forage sources

Treatment may include:

• 🌞 Complete sun avoidance for several weeks
• 💊 Anti-inflammatories to manage pain and swelling
• 🌿 Detoxification diet to support liver recovery

📲 Use Ask A Vet for Skin & Liver Support

The Ask A Vet app offers quick access to expert help for horses showing signs of sun sensitivity or liver disease:

• 📸 Upload photos of lesions for fast assessment
• 🧪 Ask about safe supplements or detox plans
• 🌱 Submit forage lists to identify risky plants
• 📋 Track symptoms and lab values over time

Get peace of mind before it becomes a serious issue. 🐴📲

✅ Sunburn vs. Photosensitization Tips for 2025

• ☀️ Sunburn usually appears on the **face and muzzle only**
• 📍 Photosensitization affects **other white-skinned areas**—often suddenly
• 🧪 Photosensitization is often a **sign of plant ingestion or liver dysfunction**
• 🔍 Don’t assume peeling skin is harmless—get a diagnosis
• 📱 Use Ask A Vet to assess risk, plants, and safe management

📲 Final Thoughts from Dr Duncan Houston

Skin reactions in horses—especially those with white or pink skin—can appear innocent at first. But if inflammation occurs outside the muzzle and eyes, **don’t brush it off as sunburn**. Photosensitization could mean your horse’s liver is in trouble—or that they’ve ingested a toxic plant. Always play it safe. 🧠💙

Download the Ask A Vet app to assess skin issues, review toxic plants, and get expert guidance on liver health and sun safety in 2025. 🐎📱