Vets examine whether we help or harm horses with frequent lathering and rinsing
When your gray comes in from the pasture as a bay or your gelding is crusty with sweat and dust after a summer ride, you reach for the hose and bucket. But is your bathing ritual giving him a top-to-bottom gleam … or is it stripping the skin of natural oils and decimating the populations of healthy microorganisms that help fight infection?
“It is amazing how often certain horses get bathed—up to three times a day in some cases, and then they are simply put back in their stalls damp,” says Lori Bidwell, DVM, Dipl. ACVAA, co-owner and founder of Kentucky-based East West Equine Sports Medicine. Bidwell has worked with thousands of performance horses and has pretty much seen it all when it comes to skin issues.
In this article, we’ll learn about the horse’s largest organ system—the skin: what it looks like, what functions it serves, and how daily primping and preening can wreak havoc on this vital structure.
You’re likely familiar with the different degrees of burns fire victims sustain. What you might not realize is that these degrees refer to the layer of skin the burn reaches.
Layer 1: The Epidermis This outermost layer produces and contains specialized skin cells called keratinocytes. They migrate upward from the base of the epidermis, continually replacing sloughed skin cells—much like our fingernails continually grow from near the cuticle and the horse’s hoof grows from the coronary band. Other cells in the epidermis include pigment-producing melanocytes that give skin and hair their color and Langerhans cells that help fight infection, playing an important role in the skin’s immune system.
Although hairs do indeed pass through the epidermis, the follicles are actually in the layer just beneath, called the dermis. Nonetheless, hairs help protect the skin from ultraviolet light and physical damage (slight abrasions, insects, mild chemicals) and facilitate thermoregulation—cooling and warming by changing their position relative to the skin.
Layer 2: The Dermis This layer, which makes up the bulk of the organ, contains a variety of structures, including blood vessels, nerves, and “skin appendages.” Its main function is to nurture the epidermis. Blood vessels supply nutrients and help regulate the horse’s body temperature. Specifically, increased blood flow to the vessels in the dermis help dissipate heat during exercise, while blood vessel constriction decreases blood flow to reduce heat loss through the skin. The nerve supply to the skin is impressive, allowing horses to rapidly respond to heat, cold, pain, and subtle pressures and touches. Our nerve supply is similar; think about the immediate reaction you have after touching a dish right out of the oven or slicing your finger on a piece of mail.
Hair follicles, one of the major skin appendages, produce the individual hairs. Ancillary appendages include sebaceous glands that produce an oily substance called sebum. Sebum protects the skin by keeping it soft, moist, and pliable. It also possesses antimicrobial properties.
Sweat glands, primarily located on the abdomen and thorax (and not the legs) also help control the horse’s body temperature. As sweat evaporates, the body cools.
Layer 3: The Hypodermis The third and final layer, found beneath the dermis, contains fat, muscle (the twitch muscles, for example, that discourage insects from landing), blood vessels, and nerves.
Life on the Surface
So, we now know this outer layer—this collection of dead skin cells covered with sebum and punctuated with hair follicles—is protective, thermoregulatory, and infection-fighting. A population of microscopic organisms on the surface of the skin lends a helping hand.
Just like the intestines are filled with millions of microbes that keep the horse healthy, the skin also has “normal” bacteria, viruses, and fungi (including yeast) residing on its epidermis. These microbes, called the skin microbiome, populate the skin’s surface during and immediately after birth. They remain with the horse for the rest of its life. As commensals—organisms that live on or in a host with both microbe and host deriving a mutual benefit—they help prevent pathogenic (disease-causing) organisms from colonizing the skin. Dozens of bacterial species inhabit the skin, including Staphylococcus spp (even S. aureus, of MRSA infamy) and Streptococcus spp. More than 30 fungi species cohabitate with the bacteria, including Aspergillus, Candida, and Malassezia. Interestingly, certain types of bacteria and fungi prefer certain regions of the skin; some species choose to inhabit the armpit and groin areas, while others frolic on the back, head, or neck.
Members of the skin microbiome can, in some cases, cause or contribute to certain skin diseases. When breaks in the skin or changes in the epidermal “environment” (the amount of sebum present, for example) occur, commensals can cause infection and/or disease.
Pros and Cons of Bathing
Depending on a horse’s use, the number of baths he gets can vary tremendously. Some of us might have to wrack our brains to recall the last time we bathed our pony, whereas others give their babies a weekly spa treatment. Others still bathe them daily or even multiple times a day.
Removing dried sweat, dirt, and debris is absolutely necessary, especially after riding. Foreign material between the horse and the saddle or boots can damage the skin, causing infection and pain and lost riding time. Grooming, not necessarily bathing, removes said debris, often preventing these insults. Routine grooming also allows us to examine our horse carefully from top to bottom for:
- Cuts, abscesses, or abrasions;
- Insect or animal bites;
- Ectoparasites, such as lice and ticks (the latter of which can transmit Lyme disease);
- Abnormal growths such as warts, sarcoids, melanomas, or aural plaques;
- Body condition changes; and more.
Soap doesn’t need to be a staple when bathing and grooming. Soap itself is a chemical produced by mixing some sort of fat (vegetable oil, rendered beef tallow, coconut oil) with a base (such as sodium hydroxide) to create a salt—a process called saponification. Consider, too, that many products marketed as soaps or shampoos contain ingredients that aren’t good-old-fashioned saponified fats.
Ponder the following ingredients in some popular equine shampoos:
- Water (also called aqua or eau);
- Sodium lauryl sulfate, a detergent that produces lather and is known to cause skin irritation in humans;
- Cocamidopropyl betaine, a coconut-derived foaming agent;
- Sodium chloride or table salt;
- Cocamide MEA, a coconut-derived product mixed with ethanolamides used to increase foaming;
- Glycol distearate, which acts as a chemical emollient to reduce moisture evaporation from skin;
- Propylene glycol for attracting water to give skin a supple look;
- Fragrance (parfum), which contains undisclosed ingredients considered “trade secrets” by the FDA;
- The preservatives methylchloroisothiazolinone and/or methylisothiazolinone that possess antibacterial and antifungal effects and might irritate the skin in high concentrations; and
- Butylphenyl methylpropional, a synthetic fragrance that’s been linked to allergic reactions and skin irritation in humans.
Using such products on occasion can certainly help your horse achieve that squeaky-clean look and feeling and remove debris, caked-on dirt, and even flakes of dry skin. Overuse (the definition of which will vary from horse to horse), however, strips the skin of its normal, healthy microbial populations as well as natural oils, primarily sebum.
Instead of leaving the skin and coat clean, soft, and smooth, some horses begin showing signs of flaking, dandruff, and pruritis (itchiness). For comparison, think about how tight, dry, and itchy your own skin can feel after a long, hot, soapy shower. Further, soaps and their “extras” can cause skin irritation or even a contact dermatitis or allergic reaction resulting in hives. Being itchy, horses will find things to scratch themselves on, potentially damaging the skin further and allowing pathogenic organisms or even the once “healthy” organisms colonizing the skin to cause disease.
“We often see dermatitis associated with Staphylococcus and Dermatophilus bacterial infections, both associated with overwashing and either destroying the protective flora or causing overgrowth of normal flora,” says Bidwell. “Owners often think there is a fungal component, but typically these skin issues are associated with Gram-positive bacteria, not fungi.”
Skin lesions are uncomfortable and can contribute to lost training or competition days. Further, depending on the severity and location, lesions can also preclude certain medical procedures from being performed. You might need to postpone joint injections, epidural analgesia, and acupuncture treatments if the skin is in bad condition.
“Infections can spread quickly,” says Bidwell. “In some cases, infections can be severe, causing cellulitis, which is a serious bacterial infection of the skin and associated tissues that can cause intense swelling and lameness. Prompt veterinary attention in these cases is warranted.”
One simple way to avoid infections is to minimize bathing with soaps and to dry a horse thoroughly following a bath. Constant moisture alone can still irritate skin, setting it up for infection. Further reason to make sure your horse is completely dry before putting him up post-rinse or -bath is that, again, hair plays an important role in thermoregulation and can’t do its job well when wet.
Putting Your Best Follicle Forward
Minimizing bathing frequency and the use of soaps and potentially harmful chemicals can help improve the overall quality and health of your horse’s skin and hair coat.
“We absolutely witness a vicious cycle,” says Bidwell. “Horses are overwashed, develop skin problems, and then get washed more to try to resolve the skin issues caused by washing them in the first place. These cases often require systemic antibiotics and minimizing water contact completely to remedy the problem.
“Instituting simple management changes like replacing regular shampoos with a very mild oatmeal aloe shampoo or eliminating shampoos altogether (or switching to a medicated shampoo if battling a skin infection), drying horses completely in the sun after bathing, avoiding topical alcohol to expedite drying following a bath, and minimizing the administration of medications that stunt the immune system, like systemic corticosteroids such as dexamethasone, can resolve these problems quickly.”
One of the signs of a healthy horse is a lustrous, gleaming coat. But remember that beauty comes from the inside. Focus on supporting a healthy integumentary system, rather than reaching for fancy bottles of shampoos and conditioners. When you do need to wash or whiten, use soaps sparingly, and keep an eye out for signs of skin issues related to overbathing.