A simple shortcut for checking if a layer is inside a LayerMask.

LayerExtensions.cs

using UnityEngine;

public static class LayerExtensions
{
    public static bool Contains(this LayerMask mask, int layer)
    {
        return (mask.value & 1 << layer) > 0;
    }
}

//Example usage
public class PoorWarrior : MonoBehaviour
{
    public LayerMask enemyLayer;
    private int health = 100;

    private void OnTriggerEnter(Collider other)
    {
        if (enemyLayer.Contains(other.gameObject.layer))
        {
            //Do something
            GetDamage(10);
        }
    }

    private void GetDamage(int damage)
    {
        if (health > 0)
        {
            health -= damage;
        }
    }
}