Public health is an important and growing field that includes a variety of potential careers, including epidemiology, biostatistics, health education, and health policy and management. Because public health is a multidisciplinary field, what you need to study before applying to a master's program will depend on what specific aspect of public health you want to pursue.
Math is important to all areas of public health. If your focus in public health will be on biostatistics, take three semesters of calculus as an undergraduate, as well as a computer programming language. Other areas of public health require a minimum of college algebra or one semester of calculus. Epidemiologist, for example, often use mathematical modeling to predict how diseases will spread throughout a population, so a solid understanding of calculus is essential.
Communication skills, verbal and written, are essential to all public health careers, especially health policy and education. Being able to write clearly and effectively is an important skill that will help you advance your education and your career, so composition and writing courses should be an important part of undergraduate preparation for a master's in public health.
Successful completion of an undergraduate course in biology is important for the fields of biostatistics, epidemiology and environmental health sciences. A chemistry background is also helpful for studies in environmental health because environmental health practitioners often study chemical pollutants and toxicology. Biology, anatomy, nutrition and other health-related sciences could inform any career in public health. Public health work often involves collecting and analyzing data that can inform decision making, so experience with scientific methodology and analysis is fundamental.
For fields like behavioral science, global health and health education, some undergraduate coursework in social sciences like psychology, sociology, education and anthropology are often recommended. For those who want to go into health policy, courses such as economics and political science would be good background, but won't be required. The social sciences will give you a background into the theories and practices that shape public health, whether it's the ability to discern the cultural practices that affect childhood health outcomes, or the economic forces that influence health care policy. Those who want to go into health management may find a background in business helpful, because budgeting, administration and personnel management are important to the field.