Researchers at Aberdeen University say more money needs to be spent on developing treatments in parts of the developing world where fungal infections kill as many people as tuberculosis or malaria.
They say there is a lack of international understanding of the problem, even though more than 50% of people who contract a severe invasive fungal infection may die from the disease.
Their findings are laid bare in a new study in Science Translational Medicine, titled Hidden Killers: Human Fungal Infections.
Gordon Brown, professor of immunology at Aberdeen and part of the university's Aberdeen Fungal Group, said: "Fungi infect billions of people every year, yet their contribution to the global burden of disease is largely unrecognised.
"It is the less common invasive fungal infections that we are concerned about. Many species of fungi are responsible for invasive infections which kill about 1.5 million people each year.
"However, the actual figure is not really known because epidemiological data for fungal infections is notoriously poor and fungal infections are often misdiagnosed. The longer it takes to detect and identify the fungus as the underlying cause of disease, the less the chance of saving the affected patient."
Statistics show there are around four cases of serious fungal infection per 100,000 people in the UK each year.
Professor Neil Gow, professor of microbiology at Aberdeen, said: "Serious invasive fungal infections can be called hidden killers because they can be contracted by people who already have another health problem which has compromised their immune systems."