Homeless people are more likely to suffer injuries and medical problems from their lifestyle on the street, which includes poor nutrition, exposure to the severe elements of weather, and a higher exposure to violence. Yet at the same time, they have reduced access to public medical services or clinics, in part because they often lack identification or registration for public healthcare services. There are significant challenges in treating homeless people who have psychiatric disorders because clinical appointments may not be kept, their continuing whereabouts are unknown, their medicines may not be taken as prescribed, medical and psychiatric histories are not accurate, and other reasons. Because many homeless people have mental illnesses, this has presented a crisis in care.The conditions affecting homeless people are somewhat specialized, and have opened a new area of medicine tailored to this population. Skin conditions, including scabies, are common, because homeless people are exposed to extreme cold in the winter, and have little access to bathing facilities. They have problems caring for their feet, and have more severe dental problems than the general population. Diabetes, especially untreated, is widespread in the homeless population. Specialized medical textbooks have been written to address this for providers.Due to the demand for free medical services by homeless people, it might take months to get a minimal dental appointment in a free-care clinic. Communicable diseases are of great concern, especially tuberculosis, which spreads more easily in crowded homeless shelters in high-density urban settings.
In fact, self-reported rates of respiratory diseases (including asthma, chronic bronchitis and emphysema) are double that of the general population.The homeless population often live in higher risk urban areas, with increased exposure and little protection from the elements. They also have limited access to clean drinking water, and other methods of cooling down. The built environment in urban areas also contributes to the "heat island effect", the phenomenon whereby cities experience higher temperatures due to the predominance of dark, paved surfaces, and lack of vegetation. Homeless populations are often excluded from disaster planning efforts, further increasing their vulnerability when these events occur. Without the means to escape extreme temperatures and seek proper shelter, and cooling or warming resources, homeless people are often left to suffer the brunt of the extreme weather. The health effects that result from extreme weather include exacerbation of chronic diseases and acute illnesses. Pre-existing conditions can be greatly exacerbated by extreme heat and cold, including cardiovascular, respiratory, skin and renal disease, often resulting in higher morbidity and mortality during extreme weather. Acute conditions such as sunburn, dehydration, heat stroke, and allergic reactions are also common. In addition, a rise in insect bites can lead to vector-borne infections. Mental health conditions can also be impacted by extreme weather events as a result of lack of sleep, increased alcohol consumption, reduced access to resources and reduced ability to adjust to the environmental changes. In fact, pre-existing psychiatric illness has been shown to triple the risk of death from extreme heat.