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Are there documented cases of skin irritation or allergic reactions from horse paste on humans?
Executive summary
There is documented concern and some clinical reporting about people using veterinary “horse paste” (ivermectin paste) on human skin, including warnings that formulations differ from human products and may contain irritants like propylene glycol; pharmacokinetics and safety of 1.87% paste applied to human skin are not established [1] [2] [3]. Dermatologists and outlets have warned that these veterinary preparations have not been tested on humans and “could pose unknown risks,” including skin irritation, but systematic case series of allergic reactions specifically from topical horse paste in humans are not described in the provided reporting [4] [1].
1. What reporters and clinicians have documented: misuse, unknowns, and explicit warnings
Journalistic and clinical accounts document a pattern of people applying horse deworming paste topically for rosacea or Demodex control, and dermatologists explicitly warn against this practice because veterinary paste is not studied or approved for human topical use; Business Insider quotes dermatologists saying it “could pose unknown risks” [4]. The British Journal of Dermatology case discussion raises the issue that veterinary ivermectin pastes (e.g., 1.87%) have unknown skin pharmacokinetics in humans and cautions clinicians about this emerging trend [1].
2. Evidence (and limits) about skin irritation or allergic reactions from the paste itself
Available sources note that some veterinary horse pastes (Duramectin and similar) contain propylene glycol, a solvent that dermatologists recognize can irritate sensitive skin; practising dermatologists have said that propylene glycol in these formulations “can irritate sensitive skin types” [2] [3]. However, the sources do not present a systematic set of published case reports documenting allergic contact dermatitis or urticaria directly caused by topical application of horse ivermectin paste on humans; the British Journal of Dermatology paper says the pharmacokinetics of 1.87% paste on human skin are unknown rather than reporting specific adverse-event rates [1]. Therefore, specific documented numbers or formal case series of allergic reactions from horse paste are not found in the provided reporting.
3. Mechanisms that make skin reactions plausible
Dermatologists point to two reasons irritation is biologically plausible: (a) non‑human formulations often include excipients (like propylene glycol) that are established skin irritants or sensitizers in some people; (b) veterinary paste concentrations (e.g., 1.8–1.87% ivermectin) differ from the 1% topical human gel (Soolantra), so both higher active dose and unknown absorption could alter local skin effects [2] [3] [1]. The clinical review in the British Journal of Dermatology emphasizes that formulations intended for animals have not been studied in humans and therefore could produce unforeseen local or systemic effects [1].
4. Reported clinician experience and anecdote: mixed signals
Some practicing dermatologists and dermatology discussion forums have anecdotal reports that patients using Duramectin have not experienced “serious adverse events” in available informal accounts, while others caution that the paste is thick, hard to spread, and can irritate rosacea‑prone skin—again largely anecdotal rather than systematic evidence [2] [3]. Business Insider reports the broader professional cautionary stance without enumerating specific documented allergic cases [4].
5. Public-health and professional concerns beyond immediate irritation
Clinical authors raise additional concerns: unregulated topical use could foster ivermectin resistance in mites or parasites, and misusing veterinary products may lead people to substitute other unstudied veterinary agents for prescribed human medicines [1]. Journalists and clinicians frame the issue not only as potential local irritation but also as a problem of unknown systemic exposure and broader consequences [1] [4].
6. What the available sources do not say (important limitation)
The assembled sources do not provide peer‑reviewed case series or epidemiological studies that quantify rates of contact dermatitis, allergic reactions, or other cutaneous adverse events from topical application of horse ivermectin paste on humans; they document warnings, pharmacokinetic unknowns for 1.87% paste, and anecdotal clinician comments [1] [2] [3]. If you need confirmed case reports or incidence data, available sources do not mention those specifics [1].
7. Practical takeaway and competing perspectives
Dermatologists and academic clinicians uniformly advise caution because veterinary pastes are untested on human skin and may contain irritant excipients; some anecdotal users report perceived benefit without major side effects, but this is not systematic evidence [4] [2] [3]. The British Journal of Dermatology urges clinicians to discourage unregulated use and to be aware of the trend due to unknown pharmacokinetics and potential resistance implications [1]. Available reporting supports a cautious, clinician‑led approach rather than off‑label self‑treatment with veterinary products [1] [4].
If you want, I can search specifically for peer‑reviewed case reports of allergic/contact dermatitis attributed to veterinary ivermectin paste since 2019, or compile professional society statements on this practice from dermatology organizations.