National rules dictate how often a person can donate blood. In the United States, for instance, donors must wait at least 56 days - 8 weeks or 2 months - between donations of whole blood. But the time period between donations varies by country.

For example, compare the following countries:

• India - The "minimum time advised" between donations is 3 months (12 weeks)
• Nigeria - Women can donate blood every 4 months (16 weeks) while men can donate every 3 months (12 weeks)
• South Africa - People can donate blood every 2 months (8 weeks)
• Brazil - Women can donate blood every 3 months (12 weeks) and men can donate blood every 2 months (8 weeks) (As of 2012)
• United Kingdom - Women donate blood every 4 months (16 weeks) and men can donate blood every 3 months (12 weeks)
• Mexico - People can donate blood every 2 months (8 weeks)
• Philippines - People can donate blood every 3 months (12 weeks)

Donation times for other blood products is unique to each country as well. The majority of blood donations are for whole blood which contains red cells, white cells, and platelets all suspended in plasma. Donations can be made just for red blood cells (frequently used in transfusions during surgeries), platelets (that help form blood clots), or plasma which all have different rules for donation frequency.

Of course, every country has eligibility criteria for blood donors including:

• Age
• Weight (minimum weigh requirement)
• Healthy iron level
• Whether or not they have an active infection
• Certain blood clotting conditions (for people whose blood does not clot normally or who are on blood thinners)
• Types of cancers
• Creutzfeldt-Jakob Disease
• Men who have sex with men (MSM)
• Ebola
• Certain heart disease conditions
• Hepatitis
• Jaundice
• Hemochromatosis
• HIV or AIDS
• Recent tattoos
• Recent travel to certain countries
• Pulse
• Pregnancy
• Sickle Cell Disease
• Tuberculosis
• And many more

Globally, blood shortages are very common in almost every country. Natural disasters, blood loss due to labor, accidents, and other blood-intensive medical procedures increase blood needs dramatically. This is why the World Health Organization requests healthy people to donate blood to their local health groups at appropriate intervals.

The majority of health systems are dependent on blood donations to operate. Without residents donating, many lives would be lost and health outcomes like mortality would be altered.