Fallout 76 alters the way radiation works: Instead of just limiting SPECIAL stats or max health, it allows the player character to develop various mutations, which act like traits in other games in the series: They give a mixture of powerful positive and negative effects. The Class Freak perk will reduce the negative effects of a mutation by up to 75%, while Strange in Numbers will grant a 25% increase to the positive effect if teammates are also mutated.
It is also possible to acquire multiple mutations at the same time, including all 19 that are currently available (the sole exception is Carnivore and Herbivore which lock each other from being acquired). However, to have all 19 active is wildly disproportionate to any playstyle and is recommended to pursue mutations that synergize with each other.
Whenever a player takes Radiation damage, they have a chance to gain a Mutation, equivalent to 5% per 5 points of radiation damage. Players cannot gain Mutations if they are below Level 5.
Serums are consumable items that will grant a specific Mutation as soon as the player uses it, and temporarily suppress the negative effects of the Mutation and increase the positive effects. If the player already has the mutation, the serum will still temporarily suppress the negative effects of the Mutation and increase the positive effects. All serums and their recipes are sold by MODUS at the Whitespring Bunker Science Wing terminal. Recipes for the serums can also be purchased from MODUS but have a steep price of 24000 caps per recipe.
Mutations are semi-permanent. Every time the player uses RadAway or a Decontamination Shower, there is a chance that a Mutation will be removed. They can keep using RadAway for more attempts to remove a Mutation. The Starched Genes perk allows for locking mutations, as it reduces/eliminates both the chance of becoming mutated and their removal chance by RadAway. These are the only ways present to remove mutations. Mutations cannot be removed through death. However, a percentage of rads is removed through each death, so it's possible to decontaminate oneself through multiple deaths if the Starched Genes is not yet acquired.
Even with the Starched Genes perk, a Mutations' effects can be suppressed for a time with the use Rad-X. The suppression lasts for approximately 10 minutes (1 hour in-game). To avoid the suppression effects of Rad-X, the diluted version can be used as it offer the benefits of it without the suppression effect.