Many diseases affect the skin, even though they aren't actual skin conditions. Health issues that affect your immune system, circulation, thyroid gland, and hormone levels can all cause skin problems. Controlling these disorders often can help your skin symptoms improve. Here's what you should know about seven such diseases. Diabetes You probably think of blood sugar levels and excess weight when you think about diabetes. However, this chronic health issue affects every part of the body, including your immune system and your skin. People with diabetes are more likely to get infections caused by bacteria or fungi, like Candida albicans. Bacterial infections may cause boils, which are pockets of infection. They can cause a sty on your eyelid. These infections can make your skin look red, hot and swollen. Fungal infections can cause itchy rashes around moist folds of skin, such as the groin and armpits. You might also notice small blisters and scales around these red rashes. In addition, people with diabetes have poor circulation. This can lead to dry, itchy skin. Diabetic dermopathy causes scaly skin patches, often on the legs, because of issues affecting your small blood vessels. Another diabetes-related skin issue is acanthosis nigricans. It shows up as dark patches on the neck, armpits and groin. Taking good care of your skin and keeping diabetes under control can help prevent these problems. Inflammatory Bowel Disease (IBD) Ulcerative colitis and Crohn's disease both involve inflammation in the digestive tract. They can cause severe diarrhea, pain, and weight loss. IBD can affect the skin, too. Some of these skin issues need a doctor's attention. You may notice: Sensitive red bumps on your skin on your lower legs, ankles and arms. The name for these is erythema nodosum. The condition often gets worse during an IBD flare. Small blisters that become deep sores. The medical name for this is pyoderma gangrenosum. Skin tags or small flaps of skin that form at the anus due to hemorrhoids. Small tears, called anal fissures, that form in the lining of the anal canal and may crack and bleed. Skin ointment and warm baths may help ease the pain and itchiness they cause. Other skin problems can be the result of medication you might take for IBD. Lack of nutrients caused by the diseases themselves also can cause skin problems. Parkinson’s Disease Skin changes are common with Parkinson’s disease—a nervous system disorder. It can lead to very oily and flaky skin, particularly on the scalp, forehead and nose. You may also develop white or yellowish skin scales. Skincare products and medications to control oily skin can help ease these symptoms. Also, some Parkinson’s medications make some people sweat more or have extremely dry skin. Thyroid Disease Both dry skin and recurring hives can be signs of thyroid disease. Hives are very itchy, red bumps or welts on your skin. They may turn white when you press in the center. Often they go away but come back in a few months or years. Hives may get worse if you scratch them, sweat, exercise or are stressed. Hives aren’t dangerous, but they can be a sign of an underactive thyroid condition that needs treatment. Drugs to control allergies and itching may help ease recurring hives. Polycystic Ovary Syndrome (PCOS) This condition causes infertility. Women who have PCOS often have skin conditions, possibly due to abnormal hormone levels. Skin problems related to PCOS include: Acanthosis nigricans—dark patches of skin on the neck, armpits, and other skin folds Acne on the face, chest and back Excess facial hair Skin tags on the neck or in the armpits Lyme Disease This is a bacterial infection spread by certain ticks. Symptoms include fever, headaches, fatigue, and joint stiffness. One sign of Lyme disease is a skin rash that looks like a big red bull's-eye. The rash may be at the site of the tick bite, but it can appear anywhere on the body. It usually isn’t itchy or painful, but it may get bigger over the course of about a week. Lyme disease and the rash usually clear up completely with prompt antibiotic treatment. See your doctor if you notice this telltale sign. HIV/AIDS HIV/AIDS weakens the immune system, which raises the risk of skin infections caused by germs, including fungi and viruses. People with HIV/AIDS may also have an abnormal skin reaction to sunlight, called photodermatitis. This may cause dark patches as well as a rash, blisters or scales on the skin. Over time, this can lead to scarring or cause skin to thicken. Wearing sunscreen and taking other steps to shield the skin from harmful UV rays can help.