Money can become a host for mold growth under specific environmental conditions. The composition of currency and the presence of moisture create an environment where these microscopic fungi thrive. Understanding how and why mold develops on banknotes, and what steps to take, helps manage this issue.
How Mold Grows on Currency
United States banknotes are not made from typical paper, but rather a durable blend of 75% cotton and 25% linen fibers. This material, similar to fabric, provides an organic food source that mold can consume. The fibrous nature of cotton and linen also makes banknotes absorbent, allowing them to retain moisture, a key factor for mold proliferation.
Mold spores are naturally present, waiting for the right conditions to grow. These conditions include sufficient moisture, often from high humidity, direct water exposure, or damp storage. Mold growth is promoted when relative humidity levels exceed 60%, with optimal conditions for germination and growth at 70-75% relative humidity sustained for several days. Warm temperatures, between 60-80°F (15.5-26.7°C), accelerate mold development. Poor air circulation and a lack of light also contribute to an environment conducive to mold.
What to Do About Moldy Money
If you discover mold on your currency, it is not advisable to attempt cleaning it yourself. Aggressive cleaning methods can further damage the banknotes or spread mold spores, which may pose health risks. Mold exposure can cause allergic reactions, respiratory irritation, and other symptoms, particularly for individuals with sensitivities or compromised immune systems. Some molds produce mycotoxins, which can lead to fatigue, headaches, or concentration difficulties.
For currency that is merely worn, torn, or dirty but largely intact (more than 50% remaining), you can exchange it at any commercial bank. Banks replace such “unfit” currency. However, for banknotes that are significantly damaged—for instance, by fire, flood, chemicals, or substantial mold growth—they are considered “mutilated currency.”
In cases of mutilated currency, where less than 50% of the note remains or its value is questionable due to severe damage, the Bureau of Engraving and Printing (BEP) offers a free redemption service. You submit the damaged currency directly to the BEP for examination by experts. They assess the authenticity and value of the remnants, and if satisfactory, a check for the redeemable amount will be issued.
Keeping Your Money Mold-Free
Preventing mold on currency centers on controlling environmental conditions, primarily moisture. Store money in dry, cool, and well-ventilated locations. Avoid keeping cash in damp areas such as basements, garages, or any place prone to leaks or high humidity.
Maintaining indoor relative humidity levels between 30% and 50% can inhibit mold growth. In enclosed spaces like safes or storage containers, use moisture absorbers or desiccants, such as silica gel packets, to reduce humidity. Ensure any money being stored is completely dry before placing it into storage. For collectible banknotes, using archival-grade, acid-free paper and PVC-free plastic sleeves or holders provides additional protection against environmental factors and chemical degradation.