I used castor oil on my eyelashes and eyebrows - it worked great! I just used a random off of Amazon, linked here. Basically I just applied it with my fingers, massaging it into my eyebrows and lashes before sleeping every night.
I don’t have any irritation with castor oil but I do with most lash serums which is why I love castor oil. A while ago i destroyed my lashes with lash extensions and I was shocked how quickly they grew back with castor oil. This is what I have been using. Cliganic USDA Organic Castor Oil, 100% Pure (8oz with Eyelash Kit) - For Eyelashes, Eyebrows, Hair & Skin | Natural Cold Pressed Unrefined Hexane-Free | DIY Carrier Oil | Cliganic 90 Days Warranty https://www.amazon.com/dp/B07Z55TTHR/ref=cm_sw_r_cp_api_glt_i_M82JJB0QAXNX100AXK45?psc=1
I bought this one from Amazon but I think they’re probably all the same. What’s funny is I read about castor oil & eyelashes 20 years ago on makeupalley but I thought it was impossible back then. 🤦♀️ 💰
Cliganic USDA Organic Castor Oil, 100% Pure (8oz with Eyelash Kit) - For Eyelashes, Eyebrows, Hair & Skin | Natural Cold Pressed Unrefined Hexane-Free | DIY Carrier Oil | Cliganic 90 Days Warranty https://smile.amazon.com/dp/B07Z55TTHR/ref=cm_sw_r_cp_api_glt_fabc_AVTRMQQ9DCADBZCB8FQA?_encoding=UTF8&psc=1