Wondering what is the red section on the dweller's health bar? Well, this is nothing but the effect of the radiation or lack of water. This will also affect your dwellers happiness, to fix this here is the guide below on how to remove the Vault dweller's Red health in Fallout Shelter.
What is Radiation damage in Fallout Shelter?
Whenever your vault is attacked by the rad roaches your dwellers take the radiation damage. The red section on your dweller's health bar is the radiation damage taken by the dweller. The more the damage higher the red will appear on the dwellers health bar. Sometimes due to lack of water the radiation damage increases.
How to cure the Radiation Damage?
Due to the Radiation damage your dwellers health is restricted. Resulting in lowering your dwellers health from maximum. As they say "For every negative impact there's positive reaction" so for Fallout Shelter to save the dwellers there are few ways to cure the damage.
Radaways:
The Radaways is used to drastically reduce dwellers red health woes(the radiation damage). The Radaways are not used to heal the dweller, but just to reduce the damage and gaining the full health bar for your dweller. To use the radaways click on the dweller you want to reduce the damage and then select the radaways icon(little I.V. bag with a radiation warning on it). You can also get Radaways from the lunchbox(Purchasing it). Or else you can also build a science lab with higher intelligence dweller assigned to it.
Note: The Science Lab will only unlock if your Vault has 16+ dwellers.
Water:
Energy, Food, and Water are the main resources you should worry about in Fallout Shelter. Energy is used to supply power to your rooms, Food to restore your health slowly and water to fight with the radiation damage/effect. But this is also a slow process as it doesn't work automatically when you shut he game. Make sure you have plenty of water stored up so that it fight with the radiation effect and brings back you dwellers Health to normal.
We recommend keeping your game open till the radiation effect is gone. Hope this Guide was helpful and all your dwellers are safe. Enjoy.