Gummosis describes the excessive oozing of a sticky, gummy substance from the bark of certain trees, most commonly those in the Prunus genus like peach, cherry, and plum. This phenomenon is a visible symptom of a tree under stress, not a disease itself. For people encountering this sticky residue, the immediate question is whether this plant distress signal poses a danger to human health. Concerns revolve around the composition of the gum, the risk of allergic reactions, and the potential transfer of underlying plant pathogens.
Understanding Gummosis: Causes and Appearance
Gummosis is the tree’s natural defense mechanism, producing a polysaccharide gum to seal wounds and prevent further damage. The causes fall into two main categories: non-living environmental factors and living biological agents. Non-living causes include mechanical injuries from gardening tools, insect borers, or environmental stress such as severe frost damage or sunscald that cracks the bark surface.
The gum initially appears as a clear, soft, or milky liquid. Upon exposure to air, it quickly turns into a thick, amber-colored, jelly-like mass. This hardened, resinous material accumulates around wounds on the trunk or branches. If the cause is a boring insect, the gum may be mixed with frass, which is fine sawdust-like insect excrement.
Biological causes involve infections by specific fungi and bacteria that enter through existing wounds. Common fungal culprits include species of Cytospora and Botryosphaeria, which cause cankers that ooze gum as the tree attempts to wall off the infection. Bacterial canker, often caused by Pseudomonas syringae, also triggers this gumming reaction, especially on stone fruit trees.
Direct Human Contact: Toxicity and Allergic Reactions
The substance that oozes from the tree is primarily composed of complex carbohydrates (polysaccharides) and organic acids. Biologically distinct from the plant’s true sap, this material is not toxic to humans. Ingestion of the dried gum is unlikely to cause systemic poisoning.
The realistic concern is the possibility of skin irritation or allergic reactions. Many natural plant exudates contain compounds that can cause contact dermatitis in sensitive individuals. This reaction typically presents as localized redness, itching, or a mild rash where the skin touched the gum.
Although the gum is not a potent skin irritant like poison ivy oil, protective gloves eliminate this minor risk entirely. The substance is chemically inert in terms of systemic toxicity. The risk of irritation is a localized response to a natural plant product.
Assessing Pathogen Risk to Human Health
The microbial agents that cause gummosis are highly specialized to infect plant cells and generally pose no threat to humans. Plant and animal pathogens require different biological mechanisms to establish infection. Examples include the bacteria Pseudomonas syringae and the oomycete Phytophthora species, which are plant-specific and incapable of causing disease in people.
The fungi contributing to gummosis, such as Cytospora species, are similarly host-specific, focusing their attack on woody tissue. However, the Botryosphaeria species warrants consideration. In extremely rare instances, these fungi can act as opportunistic human pathogens, particularly following direct inoculation into a vulnerable site.
A documented case of mycotic keratitis, a severe eye infection, occurred after the eye was wounded by a thorn carrying Botryosphaeria dothidea. This type of infection requires the fungus to be physically introduced into a compromised body site, such as a deep wound or the cornea. The risk of systemic infection from merely touching an affected tree is negligible. However, the potential for fungal spores to cause an opportunistic, localized infection in an open wound highlights the value of protective measures.
Safe Handling and Prevention Measures
Safety practices minimize the minor risks of skin irritation and opportunistic infection when interacting with gummosis-affected trees. The most effective measure is wearing impermeable gloves (nitrile or thick gardening gloves) to create a barrier against the gum and associated pathogens.
Tools used to prune or scrape affected wood should be thoroughly cleaned and disinfected immediately after use. A 10% bleach solution or commercial disinfectant spray sterilizes pruning shears, preventing pathogen spread. Always wash hands thoroughly with soap and water afterward. Avoid consuming the gum, as its purity cannot be guaranteed.