The Australian Red Cross warned on Tuesday that an increase in the number of Australians getting tattoos has put a dent in number of blood donations in the country.Those who get a new tattoo must wait at least six months before they can donate blood, due to an increased risk of infection of Hepatitis-C.The Australian Red Cross is one of 25 blood services from 21 countries calling for new donors, after seeing massive drops in recent years."Today we launched the Australian component of the global campaign, called Missing Type, to increase blood donations," said Shaun Inguanzo, from the Australian Red Cross Blood Service.In Australia, the campaign will see the letters of the main blood groups - A, B and O - disappear from iconic local brands, such as the Sydney Opera House, Qantas Airlines and Australia Post.The Red Cross said a rise in the popularity of tattoos was a major reason behind the decrease in blood donations. Other reasons include people not being aware of the need to donate blood, as well as having less free time available to donate.In Australia, the number of donors has slipped from 1.8 million in 2005 to 1.3 million in 2015, a drop of 27.6 percent.A statement from the Australian Red Cross said. "In Australia there is a particular need for 100,000 new donors this financial year to help service the growing need for plasma-based medicines that thousands of Australian patients depend on for quality of life."