You bring your horse in from the pasture on a warm August morning, pick out feet, run your hand down a hind leg — and there they are. Crusty, tight little scabs stacked up the back of the pastern that were not there last week. The old-timers at the barn will tell you exactly what it is before you finish asking: dew poisoning.
It's a fitting name, because the morning dew really is the culprit. But nothing is poisoning your horse — and once you understand what's actually happening under those scabs, it stops being mysterious and starts being fixable.
What Dew Poisoning Actually Is
Dew poisoning is the summer-pasture version of a condition veterinarians call equine pastern dermatitis — the same problem that gets called scratches, mud fever, or greasy heel depending on the season and who you're talking to. Different names, same story: the skin on the lower leg breaks down, opportunistic bacteria and fungi move in, and the body walls the fight off under layers of crust and scab.
It's more common than most owners realize. In a Swiss study of 1,861 Warmblood horses, 16% had experienced pastern dermatitis — roughly one horse in six (Mad Barn's review of the equine pastern dermatitis research). And the research notes it develops more frequently in summer, when skin spends morning after morning soaked in wet grass. That surprises people who think of it as a winter mud problem. The dew doesn't care what month it is.
What Causes It
Healthy pastern skin is a tight, waxy barrier. The problem starts when that barrier stays wet too long.
Through summer, tall pasture grass holds heavy dew well into mid-morning. A horse turned out overnight or at dawn stands belly-deep in it for hours, every single day. All that repeated soaking softens the outer layer of skin the same way your hands wrinkle and weaken in the bathtub. Add a little friction from grass stems, a fly bite or two, a nick from a stray stick — and now there are micro-cracks in skin that has lost its defenses.
That's the open door. Bacteria that live harmlessly on the surface — including Dermatophilus congolensis, the same organism behind rain rot, along with staph species — slip into the broken skin and set up shop. The body responds with inflammation, serum oozes and dries, and you get those signature crusty scabs. Each scab then acts like a little roof, sheltering the bacteria underneath while the leg gets re-soaked every morning. That's why dew poisoning lingers for weeks when it's ignored: the cycle re-feeds itself daily.
A few horses draw the short straw. White-socked legs with pink skin underneath are more vulnerable (sunlight and certain pasture plants can make pink skin extra reactive), and feathered breeds trap moisture against the pastern like a wet sock that never comes off.
What to Look For
Early dew poisoning is easy to miss under hair. Run your fingers down the back of the pastern and over the heel bulbs — you're feeling for it as much as looking for it:
Small, tight scabs that feel like dried candle wax stuck to the skin. Sensitivity when you touch or flex the area. Hair standing up in little tufts over each crust. In more advanced cases: hair loss, raw or oozing patches, swelling in the pastern, and a horse that resents having the leg handled — sometimes even a short-strided or mildly lame walk on hard ground.
Catch it at the "few small scabs" stage and you're days from clearing it. Wait until the leg is swollen and raw, and you're looking at weeks — and possibly a vet call. If a leg blows up hot and swollen, or your horse goes truly lame, get your vet involved; deep infections in the pastern are nothing to gamble on.
How to Treat Dew Poisoning Naturally
The whole battle comes down to two moves: break the moisture cycle, and protect the skin while it recovers. Here's the barn routine that works — the same one we built around our own horses.
Step 1 — Clean the leg gently, then dry it completely. Wash the pastern with a mild, sulfate-free shampoo and lukewarm water. No scrubbing, no stiff brushes — the skin is already compromised. Then dry the leg thoroughly with a clean towel. Damp is the enemy here, so take the extra two minutes.
Step 2 — Soften the scabs. Never rip them. Picking dry scabs off tears healthy skin with them and opens fresh doors for bacteria. Let washing soften them; whatever lifts easily with a towel can go, and whatever doesn't comes off on its own over the next few days.
Step 3 — Cover the area with a protective clay. This is where Restorative Clay earns its spot in the tack box. Smoothed over the pastern, it forms a breathable protective shell that keeps morning moisture out while the skin underneath calms down and recovers. The bentonite base draws and dries, witch hazel soothes the irritation, and neem backs the skin up against the microbes that started the whole mess. Clean ingredients, clinical strength — no steroids, no harsh chemicals on skin that's already angry. Reapply after the leg gets wet or every day or two until the skin is smooth and the hair is coming back.
One of our customers, Rebecca, put it better than we could: "Surprisingly wonderful clay...I have been using it on my mare's scabby hind legs, and the clay immediately calmed the area down and I'm thinking I'm even seeing new hair growth." Scabby hind legs are exactly this condition — that's the clay doing precisely what it was built to do.
Step 4 — Keep it dry between treatments. On days when the skin looks good but the grass is still soaking wet, a talc-free drying powder is your maintenance tool. A quick dusting of Restorative Powder over the pastern and heel bulbs wicks moisture and keeps the funk from re-establishing in skin folds the clay has already cleared. It's the same one-two system we use for sweat and under-tack moisture all summer.
Step 5 — Manage the dew itself. You can't turn off the dew, but you can shorten the soak. If your setup allows it, hold morning turnout until the grass dries, or rotate to a shorter-grazed paddock where dew burns off faster. Mow or graze down the tall, lush corners where legs stay wet till noon. And after every bath or hose-down, towel the pasterns dry instead of leaving them dripping.
Most mild cases respond visibly within a week of this routine. The horses that stay stuck are almost always the ones whose legs get re-soaked every morning with no barrier on the skin.
Prevention Through the Rest of Summer
Once the skin has recovered, keep the habit: a ten-second pastern check when you pick feet, powder on dewy mornings, clay at the very first sign of a crust. If you're already fighting moisture problems on more than one front — thrush in the feet from the same wet pasture, funky skin under tack — the Hoof & Skin Recovery Kit bundles Botanical Blue Clay, Restorative Clay, and Restorative Powder into one system and saves you $10 versus buying them separately. Wet-season problems tend to travel together; it helps to have the whole toolkit in the barn before they show up.
Frequently Asked Questions
Is dew poisoning the same thing as scratches or mud fever? Yes — they're all common names for equine pastern dermatitis. "Dew poisoning" usually refers to the warm-season version caused by wet morning grass, while "mud fever" gets used in winter. The skin problem, and the treatment, are the same.
How long does dew poisoning take to heal? Caught early — a few small scabs — most horses show smooth, calm skin within one to two weeks of daily care. Advanced cases with swelling, oozing, and hair loss can take several weeks and may need veterinary attention.
Can I ride my horse while treating dew poisoning? Usually, yes. If the horse is sound and the skin isn't raw where tack or boots rub, light work is fine. Skip boots or wraps over affected pasterns while the skin recovers — trapping heat and moisture against the area is exactly what you're trying to stop.
Should I pick the scabs off? No. Ripping dry scabs tears healthy skin and opens new entry points for bacteria. Soften them with gentle washing, remove only what lifts easily, and let a protective layer of clay do the work underneath the rest.
Is dew poisoning contagious to my other horses? The condition itself doesn't jump from horse to horse the way a virus does, but the bacteria involved (like Dermatophilus) can spread on shared brushes, boots, and wraps. Give an affected horse its own grooming tools and wash anything that touches the legs.
Related Reading
- Rain Rot in Horses: Causes, Signs & How to Manage It
- Insect Bites on Horses: Natural Skin Recovery With Clay
- Why Every Horse Owner Needs a Talc-Free Powder in Their Tack Box
- Spring & Summer Horse Coat Care: Bugs, Moisture & Fungal Defense
- Sweet Itch in Horses: What It Is and Natural Ways to Manage It
