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What are the potential side effects of using horse paste on human skin?
Executive Summary
Using veterinary ivermectin “horse paste” on human skin carries a mixture of documented topical risks seen with approved human formulations and additional hazards unique to veterinary products: skin irritation, allergic reactions, eye irritation, and systemic toxicity if absorbed or misused, while some clinical dermatology literature supports topical ivermectin safety when formulated and dosed for humans. Approved topical ivermectin products have a generally good safety record for specific human uses; veterinary pastes are not tested for human cutaneous application and have variable concentrations and excipients that raise the risk of adverse effects and overdose. Policymakers, clinicians, and poison-control data converge on advising against self-application of veterinary ivermectin and to seek medical guidance [1] [2] [3].
1. Why people try horse paste — and what claims they repeat
Public interest in using veterinary ivermectin on people rose sharply during the COVID-19 pandemic as an off-label attempt at prevention or treatment; proponents cite ivermectin’s antiparasitic and anti-inflammatory properties documented in dermatology and tropical-medicine literature. Clinical reviews note ivermectin’s broad-spectrum activity and relative safety in approved human topical formulations, such as 0.5% lotion for rosacea and lice, which fuels perceptions that any ivermectin product must be safe on skin. However, veterinary formulations differ in dose strength and inactive ingredients, and off-label use has been associated with poison-control calls and clinical toxicity reports, undercutting the claim that horse paste is an acceptable human treatment [1] [4].
2. What the clinical literature says about topical ivermectin safety
Dermatology and infectious-disease reviews report that topical ivermectin used in regulated human formulations is generally safe, with adverse reactions typically limited to local effects such as redness, itching, burning, dry skin, and occasional ocular irritation when used near the eyes. These sources also record systemic side effects for oral ivermectin and rare laboratory abnormalities, but emphasize that properly formulated topical preparations have been used safely in large-scale programs and clinical practice. That safety profile applies to human-approved concentrations and vehicles, not to veterinary pastes with higher concentrations and untested excipients [1].
3. What toxicology and poison-control data reveal about veterinary formulations
Toxicology case series and poison-control surveillance show clear harms linked to misuse of veterinary ivermectin, predominantly when ingested but also relevant for nonstandard topical use because veterinary products contain higher doses per gram and additives not evaluated for human skin exposure. Reported harms include neurotoxic effects (dizziness, altered mental status, seizures in severe cases), gastrointestinal symptoms, and skin rashes, with veterinary-formulation cases demonstrating higher severity than prescription tablets. Public health advisories cite increased emergency calls and clinician reports that animal formulations pose a higher risk of toxicity and morbidity when used by people. These data frame veterinary paste as a documented safety hazard, not merely a theoretical concern [3] [5] [4].
4. Pharmacology and formulation differences that change risk on skin
Pharmacokinetic studies in animals and reviews explain that formulation and route of administration markedly affect absorption and systemic exposure: pour-on and paste products for animals are developed for species-specific dermal or oral delivery and can include solvents and carriers that increase penetration or deliver higher total drug loads than human lotions. Human topical ivermectin was developed to minimize systemic absorption while achieving local therapeutic concentrations; veterinary pastes lack those controls. Therefore, even confined skin application of a concentrated veterinary paste could cause unexpected local irritation or greater systemic uptake, especially on damaged skin or when used over large areas [6] [7].
5. Reconciling divergent views and practical takeaways for clinicians and the public
Two realities coexist: regulated topical ivermectin for humans has an established, generally favorable safety record when used appropriately, while veterinary ivermectin carries measurable risks documented by poison centers and toxicology reports. Clinicians should counsel patients that product origin and formulation matter: human-approved creams and lotions are the evidence-based option for approved indications; veterinary pastes are untested for human use and have led to harms. Public-health messaging should emphasize medical consultation, discourage self-treatment with animal products, and rely on poison-control and toxicology data when assessing exposures [1] [3] [5].
6. Unanswered questions and where to look next
Important gaps remain: direct studies of transdermal absorption and local-cutaneous tolerance of specific veterinary ivermectin pastes on human skin are lacking, so risk estimates must rely on pharmacology, formulation differences, and clinical toxicology reports. Further research could quantify dermal penetration from animal formulations, identify hazardous excipients, and determine thresholds for systemic toxicity from topical misuse. Meanwhile, clinicians should report adverse events to poison centers and regulators to improve surveillance, and patients should be steered to approved human products and professional care rather than self-applied veterinary ivermectin [6] [3].