Allergies are the result of a hypersensitive immune system. The allergic immune system misidentifies an otherwise innocuous substance as harmful, and then attacks the substance with a ferocity far greater than required.
Laying off an employee is different from firing an employee. Firing means letting a worker go for any reason, whereas a layoff refers to an employment termination based on economics, usually involving more than one worker.
Employers also may not use layoffs as an excuse to get rid of employees for illegal reasons. For instance, it would be illegal for an employer to select an employee for lay off because the employee had complained of hazardous working conditions.