Chemical Irritant Dermatitis
Chemical irritant dermatitis describes inflammation of the skin as a result of contact with some irritating substance. Most chemical irritant dermatitis is an reaction to products such as shampoo, liniments, sweats or rubs, tack cleaning substances etc... Other causes include caustic chemicals, urine or some bedding materials. Whatever the causative agent, the mechanism of disease is similar. The foreign substance changes the properties of the epidermis causing its barrier properties to change. Generally, there is a reduction in the amount of fats in the epidermis causing damage to cell membranes, coupled with a loss of the keratinised layer leading to a loss of water in the extracellular space. Once the cause is removed it takes a few days for most cases of chemical irritant dermatitis to clear. The application of soothing topicals may speed the recovery but be careful that those substances do not aggravate the condition.
Physical Irritant Dermatitis
This type of dermatitis is caused by prolonged between the skin and another surface. The friction causes physical damage to the epidermal cells promoting loss of the barrier capabilities of the epidermis. Friction also results in the production of heat which results in hyperemia and the local release of histamine. If friction is excessive or is sustained for extended periods it may result in ulceration and excoriation of the skin as the damage progresses deeper into the dermis. If ulceration occurs there is an increased risk of secondary bacterial infection.
Allergic Dermatitis
Allergic dermatitis is caused by a type hypersensitivity reaction to some agent in the horse’s environment or to some substance the horse has taken in. If the reaction occurs immediately upon contact with a substance, then it is a type I reaction. Common irritants include bedding materials and some plants. Some medications or vaccinations result in allergic dermatitis. There is generally a delay between the administration of the medication and the onset of the skin reaction. In such cases a type IV hypersensitivity reaction is occurring. Similarly, some feeds cause a type IV reaction in the skin resulting in the formation of wheals or rashes. In the case of delayed hypersensitivity reaction, it is sometimes difficult to isolate the causative agent as there can be a delay of up to seventy-two hours between exposure and the appearance of clinical signs. If the reaction to a feed or medication is immediate and systemic then the horse is experiencing and requires emergency care. or type
Photosensitive Dermatitis
Photosensitivity is a result of the ingestion of compounds that are stored in skin cells. These chemicals are reactive to UV radiation and cause changes in the membranes of cells. Photodynamic compounds are commonly found in buttercups, alsike clover, some NSAID’s, some antihistamines, and some hormones, and in sulphur pills. Most of these substances must
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