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Moumoujus

PYRETHRINS.

Avoid CAS 8003-34-7 / NOT REPORTED

Pyrethrins are naturally occurring compounds primarily recognized for their potent insecticidal and parasiticidal properties. While effective in treating infestations such as head lice and scabies at specific concentrations, their mechanism of action on nerve cells poses significant irritancy and severe health risks for human dermal exposure.

Summary

Science

Mechanism of Action

On a cellular level, pyrethrins excite the nervous system by prolonging the activation and opening of voltage-dependent sodium channels within nerve membranes. This leads to sustained depolarization and constant nerve excitement. In humans, this mechanism can induce paresthesias (tingling or numbness) and direct skin irritation, although humans are generally less sensitive than insects.

Research

Clinical Evidence

Low confidence
Effective range N/A
Optimal

N/A

Key findings

  1. 01 Effective for topical treatment of head lice when combined with 3% piperonyl butoxide.
  2. 02 Recommended for treatment of scabies in an ointment formulation, noting only a few cases of dermatitis.
  3. 03 Caused severe shortness of breath, cardiopulmonary arrest, and death in a 37-year-old female with a history of mild asthma, when used in a dog shampoo.
  4. 04 Caused a severe acute asthmatic attack and death in an 11-year-old girl with diagnosed asthma, when used in a dog shampoo.

Transparency

Dusting Analysis

Commonly dusted
Min. effective
0.06%
Red flag below
0.06%

Fatalities associated with severe asthmatic attacks and cardiopulmonary arrest have been reported at concentrations as low as 0.06% and 0.2% in pyrethrin-containing products. This indicates a high potential for severe adverse reactions, especially in sensitive individuals such as asthmatics, even at very low percentages.

The Formula

Formulation

Solubility
Oil
Optimal pH N/A
0 7 14

Stability

Pyrethrins are highly unstable, undergoing rapid oxidation and inactivation in the presence of light, moisture, and air. Stability decreases with higher purity. They are hydrolyzed in water, a process accelerated by both acidic and alkaline conditions. Pyrethrin I and II exhibit greater stability at lower pH, with significantly reduced hydrolysis half-lives at pH 8 compared to pH 7. In the absence of light at ambient temperature, they can remain stable for over 10 years.

Conflicts

  • Alkalies
  • Light
  • Moisture
  • Air (oxidation)
  • Acutely inflamed skin or raw, weeping surfaces

Safety

Safety Profile

CIR Status
Not reviewed
Sensitization risk High

Although generally considered low in toxicity to mammals, pyrethrins are a high irritant, causing tingling, numbness, burning, stinging, or warmth upon skin contact. Allergic reactions, including contact dermatitis, erythema, pruritus, urticaria, edema, and eczema, are possible, particularly in individuals sensitive to ragweed pollen. Fatalities linked to severe asthmatic attacks have been reported in asthmatics exposed to pyrethrin-containing products, even at low concentrations. The FDA regulates pyrethrins in specific head lice products. The EPA classifies pyrethrins as a 'possible human carcinogen' based on high-dose animal studies, although IARC categorizes them as 'not classifiable as to their carcinogenicity to humans' (Group 3). Infants and young children may be at increased risk of toxicity due to easier skin penetration.

Your Skin

Skin Compatibility

No Normal
No Dry
No Oily
No Sensitive
Irritancy High
Comedogenicity Unknown

Our Assessment

Verdict

Avoid

Given its high irritancy, significant risk of allergic reactions, documented fatalities at low concentrations, lack of established skincare benefits, and primary classification as a pesticide, pyrethrins are unsuitable for precision skincare formulations.

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