TLDR Intralesional triamcinolone acetonide is more effective but has a higher relapse rate than platelet-rich plasma for treating alopecia areata.
This study compared the efficacy of platelet-rich plasma (PRP), intralesional triamcinolone acetonide (ILS), and intralesional normal saline (NS) in treating moderate to severe alopecia areata (AA) in 75 patients. The ILS group showed the highest improvement in hair regrowth with a 63.15% reduction in SALT score, followed by the PRP group with a 37.51% reduction. ILS also had a faster response within 4 weeks compared to PRP's 8-12 weeks. However, the ILS group had a higher relapse rate (21.7%) compared to the PRP group (4.1%). Both treatments were safe with no significant adverse effects.
March 2023 in “Medica Hospitalia: Journal of Clinical Medicine” 
January 2023 in “Clinical dermatology review” Intralesional triamcinolone acetonide is better than PRP for treating scalp alopecia areata, leading to faster and more complete hair regrowth.
September 2022 in “Journal of Ayub Medical College Abbottabad” Steroid injections are more effective than platelet rich plasma for treating patchy hair loss.
24 citations
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February 2021 in “Dermatologic Therapy” Platelet-rich plasma (PRP) is a safe and potentially effective way to treat hair loss, especially when combined with minoxidil.
8 citations
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November 2020 in “Indian Dermatology Online Journal” 
7 citations
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July 2019 in “International journal of research in dermatology” Intralesional triamcinolone acetonide is more effective than platelet-rich plasma for treating scalp alopecia areata.
15 citations
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January 2016 in “Journal of Dermatology and Dermatologic Surgery” Mixing platelet-rich plasma with triamcinolone acetonide can potentially improve hair regrowth in alopecia areata patients.
74 citations
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July 2015 in “Asian Journal of Transfusion Science” Platelet-rich plasma (PRP) injections can effectively increase hair density and thickness in people with androgenic alopecia, without major side effects.
