Cannabis is an organic plant material susceptible to colonization by various molds and fungi. These microscopic organisms thrive when environmental conditions, such as temperature and moisture, are not properly controlled during cultivation, curing, or storage. When moldy cannabis is combusted and inhaled, both spores and toxic byproducts are introduced directly into the respiratory system. The potential health consequences range from mild allergic reactions to severe, life-threatening fungal infections, making proper identification and storage highly important for consumer safety.
Recognizing Mold Contamination
Identifying mold on cannabis requires a close visual inspection, as early contamination can be mistaken for the plant’s natural resin glands, known as trichomes. Healthy cannabis buds are covered in crystalline trichomes, while mold typically appears as a dull, fuzzy, or powdery layer. Look for patches of white or gray fuzz that resemble a cotton-like or spiderweb-like structure, which indicates active fungal growth.
The presence of dark spots or a grayish-black discoloration on the flower is another sign of mold, particularly in the dense interior of a bud. Unlike the appealing aroma of terpenes, moldy cannabis often emits a distinct musty, damp, or mildew-like smell. Severe contamination may produce an unpleasant ammonia-like or stale odor that is noticeably different from the typical cannabis scent.
Health Risks of Ingesting Mold and Mycotoxins
Smoking moldy cannabis poses a risk because the high heat of combustion does not destroy all harmful components, specifically microscopic spores and toxic compounds. Molds produce secondary metabolites known as mycotoxins, which are chemical substances that survive the heat of a flame and can still be inhaled. These mycotoxins, such as aflatoxin and ochratoxin A produced by species like Aspergillus flavus, are toxic to humans and can cause damage to organs like the liver and kidneys.
For a person with a healthy immune system, inhaling mold spores might cause mild symptoms like throat irritation, coughing, or wheezing. Mold-sensitive individuals may also experience acute allergic reactions, manifesting as sinus pain, congestion, or persistent nausea and vomiting. The most severe dangers are linked to inhaling spores from specific molds, most notably species of the genus Aspergillus.
Inhaling Aspergillus spores can lead to Aspergillosis, a serious fungal infection that primarily affects the lungs. While a healthy immune system can typically destroy the inhaled spores, this fungus presents a significant threat to specific populations. Immunocompromised individuals—such as those undergoing chemotherapy, organ transplant recipients, or those with HIV/AIDS—are at the highest risk of developing invasive Aspergillosis, a condition that can be severe or fatal.
People with pre-existing respiratory conditions, including asthma, Chronic Obstructive Pulmonary Disease (COPD), or cystic fibrosis, also face an elevated risk of severe lung inflammation or infection. The spores can colonize the airways, leading to chronic respiratory issues and a worsening of underlying lung function. For these reasons, consuming any cannabis product showing signs of mold is strongly discouraged.
Safe Handling and Storage Practices
Preventing mold growth is the most effective way to ensure the safety and quality of cannabis products. Mold thrives in high moisture environments, making relative humidity (RH) control the most important factor for safe storage. The optimal RH range for preserving cannabis flower while inhibiting fungal growth is between 55% and 62%.
Storing cannabis above 65% RH creates a moisture-rich environment where common molds like Aspergillus can rapidly proliferate. The flower should be kept in an airtight container, with glass jars being a preferred option, as they do not leach chemicals and provide an effective barrier against external moisture. To maintain the ideal humidity level, two-way humidity control packs can be placed inside the container to absorb excess moisture or release it as needed.
Temperature control is also important, as warm conditions accelerate both moisture evaporation and mold growth. Cannabis should be stored in a cool, dark location, ideally between 60 to 70 degrees Fahrenheit, and kept away from direct sunlight. Fluctuations in temperature should be avoided, as they can cause condensation to form inside the container, providing the necessary moisture for spores to germinate and spread.