Lichen is a common organism frequently observed on trees, often sparking questions about its potential impact on human health. Given its sometimes unusual appearance, people may wonder if tree lichen poses any risks. This article clarifies these concerns, providing information about lichen and its interaction with humans.
What Exactly Is Lichen?
Lichen is not a single organism but a stable symbiotic association, primarily between a fungus and a photosynthetic partner, typically green algae or cyanobacteria. This partnership allows them to thrive in diverse environments, from tree trunks and rocks to fences and even Antarctica. The fungal component provides structure, protection from drying out, and an anchor, while the algal or cyanobacterial partner produces food through photosynthesis, converting sunlight into carbohydrates that nourish both organisms.
Lichens exhibit various forms, including crusty patches, leafy structures, or branched, shrub-like growths. Their colors range from common gray-green to vibrant yellow, orange, or even red. Lichens grow slowly and can live for decades or even centuries. They play a role in ecosystems, sometimes serving as a food source for animals like reindeer and acting as indicators of air quality due to their sensitivity to pollutants.
Addressing Direct Human Health Concerns
Lichens found on trees are generally not considered harmful to humans. They are not inherently toxic or dangerous in typical interactions.
Accidental ingestion of small amounts of lichen is unlikely to cause serious harm. While not a common food source, some species may cause mild gastrointestinal upset if consumed in large quantities. Lichens are not acutely poisonous, but it is generally not recommended to eat wild lichens due to the possibility of encountering a species with mild toxins.
Direct skin contact with lichen typically does not cause irritation for most individuals. While rare cases of mild allergic reactions have been reported in highly sensitive individuals, often involving specific lichen acids, these instances are uncommon and usually result in minor skin irritation. Such reactions are more frequently associated with prolonged or repeated exposure, such as through contact with products containing lichen extracts.
The risk of airborne lichen particles or spores causing respiratory issues in humans is minimal compared to more common allergens. While lichens produce spores, they are not typically a significant source of airborne allergens like pollen or mold spores that trigger widespread respiratory problems. Concerns about respiratory issues from lichen are largely unfounded.
Distinguishing Lichen and Safe Interaction
Differentiating lichen from other growths on trees, such as moss or mold, helps understand their nature. Lichens are distinct from mosses, which are true plants with stems and leaves, typically softer, spongier, and green when moist. Lichens, conversely, are a symbiotic combination of a fungus and an alga or cyanobacterium, lacking true roots, stems, or leaves, and displaying a wider range of colors and textures. Mold, a type of fungus, usually appears as fuzzy, powdery, or slimy patches and can sometimes be harmful, unlike lichens. Lichens do not penetrate tree bark or draw nutrients from the tree, only using the surface as a place to grow.
When interacting with natural environments, it is prudent to avoid intentionally ingesting any wild plant, fungus, or lichen unless positively identified by an expert as safe for consumption. If handling natural growths, washing hands thoroughly with soap and water afterward can help minimize exposure to potential irritants or allergens, ensuring general hygiene. Lichens themselves pose no significant threat to human health, despite their unusual appearance sometimes leading to mistaken beliefs about their harmfulness.