In most cases, you don't need to see a doctor for poison ivy. It's okay to treat it at home! However, you might visit a doctor if your rash covers a large area, the symptoms interfere with your daily life, or the rash doesn't go away after 2-3 weeks.  For example, a large area might mean your entire calf or forearm. You should always see a doctor if the rash is on your face or genitals. Your doctor may prescribe an oral corticosteroid, such as Prednisone, if you're experiencing extreme itching. It might also be an option if your rash covers a lot of your body. However, this medication isn't right for everyone, so your doctor might recommend sticking to over-the-counter options.  Corticosteroids can cause side effects, so you should only use them as needed. The most common side effects with short-term use include sleeping issues, appetite changes, and mood issues.  Follow all of your doctor's directions for taking the medication. You likely won't need an antibiotic, but the doctor may prescribe one if your rash becomes infected. It might become infected if your skin is broken, so see your doctor if this occurs. Scratching increases your risk of developing an infection, since you can break the skin. Do not scratch your rash!

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Write a summary of the previous text in Chinese:
如果症状很严重或皮疹迟迟不消退，一定要寻求紧急治疗。 询问医生是否可以使用口服皮质类固醇来缓解严重瘙痒。 如果患处受感染，医生会给你开抗生素。