The safety of using koyo (medicated plasters) during pregnancy, especially on the head, is a concern for many expectant mothers. Most koyo products contain ingredients like methyl salicylate and camphor, which, when absorbed through the skin, could potentially pose risks to the developing fetus. It's crucial to consult with a healthcare professional or doctor before using any topical medications during pregnancy to determine if it's safe for your specific situation. Alternative remedies, such as gentle massage or warm compresses, might be safer options for relieving headaches or muscle pain during pregnancy.