Scabies: Recurrence, Allergies, and Treatment Options - Dermatology

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Scabies, caused by the Sarcoptes scabiei mite, is a highly contagious skin condition characterized by intense itching and a rash. Understanding the recurrence of scabies, potential allergic reactions, and treatment options is crucial for effective management.
1. Determining Recurrence vs. Allergic Reaction:
After treatment for scabies, it is not uncommon to experience itching for several weeks. This can be due to two primary reasons: a recurrence of the infestation or an allergic reaction to the dead mites and their waste products. To differentiate between the two, consider the following:
- Timing: If you notice new burrows or rashes appearing within a few days to a week after treatment, it may indicate a recurrence. However, if the itching persists without new lesions, it could be an allergic response.

- Symptoms: Recurrence typically presents with new lesions and intense itching, while an allergic reaction may lead to localized itching and irritation without new burrows.

- Consultation: It is advisable to consult a healthcare professional for an accurate diagnosis. They may perform a skin scraping to confirm the presence of mites.

2. Continuing Treatment with Permethrin (息疥):
If you suspect a recurrence, you may consider reapplying permethrin cream. The standard recommendation is to apply it to all affected areas and leave it on for 8 to 14 hours before washing it off. It is typically applied once, and a second application may be necessary after one week if symptoms persist. However, it is essential to follow your healthcare provider's instructions regarding the duration and frequency of application.

Regarding concerns about permethrin being neurotoxic, it is important to note that while permethrin is a neurotoxin to insects, it is generally considered safe for human use when applied as directed. The risk of significant neurological effects in humans is minimal, especially when used topically and in appropriate doses. However, if you have specific concerns or experience unusual symptoms, it is best to discuss these with your healthcare provider.

3. Alternative Treatments:
If permethrin is not effective or if you have concerns about its use, there are alternative treatments available:
- Ivermectin: This oral medication is effective for scabies and may be prescribed in cases of crusted scabies or when topical treatments fail.

- Benzyl benzoate: Another topical treatment option that can be effective against scabies.

- Crotamiton: This is another topical option that can relieve itching and kill mites.

4. Preventing Recurrence:
To prevent reinfestation, it is crucial to treat all close contacts simultaneously and to wash all clothing, bedding, and towels in hot water. Items that cannot be washed should be sealed in plastic bags for at least 72 hours to kill any remaining mites.

In conclusion, if you suspect a recurrence of scabies or are experiencing prolonged itching, it is essential to consult a healthcare provider for an accurate diagnosis and appropriate treatment plan. They can help determine whether you are dealing with a recurrence or an allergic reaction and guide you on the best course of action. Always follow the prescribed treatment regimen and take preventive measures to avoid reinfestation.