The wet/dry cycles common in milder climates can lead to scratches, a painful bacterial infection of the skin on the back of the pasterns. | Adobe StockA horses coat can only look its best when the skin beneath is healthy. Thats why an essential part of any grooming routine is staying alert to environmental conditions that can compromise dermatological health. Here are the three most common skin-compromising scenarios.1. MoistureFor starters, be on watch for rain rot, the crusty, painful skin infection that thrives in damp weather. The bacteria responsible,Dermatophilus congolensis,normally reside on your horses skin without consequence. But wet weatherparticularly following a long dry spell allows them to flourish. This overgrowth triggers an inflammatory response in the top layers of the skin and hair follicle.The earliest signs of rain rot are warmth in the affected area and hairs that stand slightly on end. Within a few days scabs begin to form at the base of the hairs. As these scabs proliferate, they develop a tight, painful crust that follows the runoff pattern of rain across a horses back and rump.Most cases of rain rot can be treated with medicated shampoosusually containing Betadine or chlorhexidineor other topical treatments specifically formulated to kill bacteria. In severe cases your veterinarian might recommend systemic antibiotics. Otherwise, the treatment protocol involves removing the scabs to kill the bacteria beneath them.The wet/dry cycles common in milder climates can also lead to scratches, a painful bacterial infection of the skin on the back of the pasterns. Scratches begins when repeated exposure to moisture followed by drying causes the skin in this area to chap and crack. Bacteria invade these small openings and, once infection takes hold, the affected skin begins to ooze and crust over, forming hard, painful scabs. Cases can range from mildeasily overlooked during routine groomingto severe enough to cause lameness.Whentreating scratches, resist the urge to pick at the scabs. Pulling them off is extremely painful for the horse and could put you at risk of being kicked. Instead, gently trim the pastern hair and wash the area with an antiseptic shampoo. Afterward, dry the skin thoroughlyusing a hair dryer if needed. Finish by applying an antibiotic ointment followed by a thick layer of an emollient cream, such as one used to treat diaper rash. Repeat this process every other day, and typically the scabs eventually loosen and fall off on their own.2. SunYoull also want to be aware of the damage sun can do to your horses skin. While we might not always think of horses as vulnerable to sunburn, they can be. Pink skin under white markings is especially susceptible because it contains less of the protective pigment melanin. A horses sunburn looks much like your ownthe skin becomes inflamed, red, and tender to the touch.Extended exposure to ultraviolet (UV) light can also lead to the development of squamous cell carcinoma. These lumpy, inflamed tumors most often form on pink skin around the eyes or genitalia. They usually do not metastasize, meaning they are unlikely to spread to other organs, but they can become locally invasive. Left untreated, squamous cell carcinomas can become large and ulcerated (raw) and be very difficult to cure.And while its not technically sunburn, ingestion of certain plants or medications combined with sun exposure can also lead to a painful condition called photosensitivity. In primary photosensitivity, a horse ingests plants containing photodynamic chemicals. When sunlight reaches these compounds through pink skin, they activate and damage the tissue, leading to swelling, blisters, and eventually tight crusts that slough off in sheets. In secondary photosensitization, liver disease prevents the horse from filtering these compounds from the blood. The resulting skin reaction is the same.You can shield a horses skin from sun in a number of ways: By providing shelter and with UV blocking masks and garments. You can also use topical sunblocks, such a zinc-oxide cream, directly on areas of pink skin. These products tend to be thick and messy but provide good protection from the sun and are easily spread over fleshy areas. For spots with thicker hair, try a nongreasy sunscreen specially formulated for horses.3. InsectsInsects are more than just annoying; their bites can trigger serious and long-lasting reactions in your horses skin. One of most significant is insect bite hypersensitivity, commonly called sweet itch. An allergic reaction to the saliva of certain biting insects, particularly tiny midges of the Culicoides species, sweet itch causes swelling and intense itchiness. Horses may rub themselves raw seeking relief. Areas where the insects like to feedthe chest, midline, crest and top of the tailsustain the most damage.Researchers have shown that horses of some breeds have a genetic predisposition to develop the condition, with Icelandic, Shetland and Friesians being most susceptible. Sweet itch often gets worse as a horse ages.Its impossible to keep all flies away during the summer months, but do your best with the use of fly sprays, masks, sheets, and boots. Also consider the larger environment, making sure youre managing manure properly and that standing water isnt an issue. If you can, keep sensitive horses indoors during insects prime feeding hours, which are usually dawn and dusk. A stall outfitted with window screens and a fantiny insects find it hard to fly in a breezeis ideal but, failing that, any shelter you can provide during those crucial hours will be helpful.