After the hepatitis B vaccination, hard knots may appear on the arms, which may last up to 1-2 weeks to subside and may subside in as little as three days. How long it takes for the hard knots to subside is mainly determined by the reasons for the hard knots, as follows: 1. 2-3 days: the hard knots produced at the injection site, mainly because the nurse may be shallow when giving the injection and there are deposits of local drugs, such hard knots can be eliminated in 2-3 days. 2. about two weeks: the T-cell immunity is produced after the vaccination and the hard knots are produced locally, such hard knots may disappear more slowly and may They may last for about two weeks, and the longest one month or more before they completely disappear. If the treatment is not carried out in time, you will feel very uncomfortable. It is recommended that you can use a clean towel dipped in hot water and apply a local hot compress twice a day for 15 minutes each time to promote the elimination of hard nodes as soon as possible.