What would the punishment be for carrying mace or pepper spray in Massachusetts?

pepper spray is legal.

Massachusetts State Pepper Spray Laws
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It is illegal for pepper spray to be mailed to Massachusetts, but it may be lawfully carried by private citizens. Before it is is legal for any resident of the state to purchase the spray, however, you must obtain a Firearms Identification Card (FID). These are very easy to get: you simply request one at any local police station, fill out the required form and provide two separate types of identification. Every FID has a processing fee of $2, and takes about a week to receive.

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More Details on Massachusetts Self Defense & Pepper Spray Regulations
Massachusetts is one of the few states that does not allow mace or any other type of defense spray to be sent in through the mail. No one other than an authorized dealer may receive any type of defense spray via the postal service. Nearby states do permit sprays that are used for personal protection to be shipped in following an online purchase, so those who live just outside MA may or defense spray products online.

Only a licensed firearm dealer has the authorization to sell self defense sprays in Massachusetts, and most do keep them in stock. Once you know where to buy them, there are a few other rules to keep in mind. There is only one acceptable use for pepper spray, and that is for the self defense of any individual who is being assaulted or threatened by an assailant. It is against the law to spray a person or animal unless your safety or the safety of someone you are with is in jeopardy. Animal pepper spray is also legal in MA, but state regulations prohibit using them for any other reason than to guard yourself against an attack. When people think of the state, they may most often bring to mind a large city such as Boston, but there are many outdoor areas where an attack from a wild animal might occur. The powerful ingredients in these sprays will incapacitate them for a short time and give you the opportunity to get away safely. Though they are safe for use on any creature, it is unlawful to use this type of spray on humans.