### Date : 2025-04-05 20:12 ---- Both **intradermal** and **intramuscular** applications of **botulinum toxin (BoNT)** have been studied for treating alopecia, particularly **androgenetic alopecia (AGA)**. Here's how they compare, based on current research: --- ### 🧪 **Mechanisms and Differences:** #### **Intradermal Injection:** - **Target**: Directly into the dermis of the scalp. - **Mechanism**: May affect **neurogenic inflammation**, modulate **cytokine levels**, and influence **hair follicle immune responses** (e.g., in alopecia areata). - **Use case**: More often explored for **alopecia areata** and **localized scalp inflammation**. - **Evidence**: - A study on alopecia areata found **no clinical benefit** of intradermal BoNT for severe forms like totalis and universalis [(Cho et al., 2010)](https://consensus.app/papers/treatment-effects-of-intradermal-botulinum-toxin-type-a-cho-lew/5c65404d599c5c9e8ee30039466630ce/?utm_source=chatgpt). - Another study also confirmed **lack of effect in recalcitrant cases** [(Thuangtong, 2017)](https://consensus.app/papers/intralesional-botulinum-toxin-a-injection-for-thuangtong/cc91a355d7a459c6909b2050789e8af5/?utm_source=chatgpt). #### **Intramuscular Injection:** - **Target**: Muscles surrounding the scalp (e.g., frontalis, temporalis, occipitalis). - **Mechanism**: **Relaxes scalp muscles**, increases **blood flow and oxygen delivery** to hair follicles, reduces **DHT conversion**, and enhances nutrient delivery. - **Use case**: Most commonly used for **androgenetic alopecia** in men and women. - **Evidence**: - Studies consistently show **increased hair count**, density, and patient satisfaction [(Zhou et al., 2020)](https://consensus.app/papers/effectiveness-and-safety-of-botulinum-toxin-type-a-in-the-zhou-yu/6eaa26a7ee06590da547958773648169/?utm_source=chatgpt), [(Singh et al., 2017)](https://consensus.app/papers/a-pilot-study-to-evaluate-effectiveness-of-botulinum-toxin-singh-neema/b8a5fb571372597bb68c8f21aed0e5e7/?utm_source=chatgpt), [(Cheng et al., 2025)](https://consensus.app/papers/effects-and-safety-of-botulinum-toxin-injection-in-cheng-cai/422aaac2708d50e48d3e291b2c3252a9/?utm_source=chatgpt). - In combination with finasteride, **results were even better**, suggesting a synergistic effect [(Zhou et al., 2020)](https://consensus.app/papers/effectiveness-and-safety-of-botulinum-toxin-type-a-in-the-zhou-yu/6eaa26a7ee06590da547958773648169/?utm_source=chatgpt). --- ### ✅ **Conclusion:** - **Intramuscular injections** are more effective for **androgenetic alopecia**, especially when targeting scalp tension and poor circulation. - **Intradermal injections** may have limited use and are currently **less supported by clinical results**, particularly in severe autoimmune forms like alopecia totalis.