An overactive immune system is equally harmful to health. Autoimmunity occurs when the immune system mistakenly targets one of the body's own normal components. This can lead to serious consequences. The human disease multiple sclerosis is an autoimmune disorder, and there are many others. It is important to note that the thyroid gland is largely responsible for regulating the rate of protein production in the body.
Underactive thyroid means a slower rate of protein production.
Because the skin and coat are made up of so much protein, hypothyroidism often results in coat loss or thinning. The body's physiology is full of cycles like these that must be borne in mind as treatment is designed. Fortunately, hypothyroidism is easy to treat, so that part of the cycle can be broken once proper testing has established a hypothyroid diagnosis. Allergies also represent an overactive immune system, at least initially. The body mounts a vigorous immune response to a relatively harmless foreign substance, like pollen or dust or a diet component.