C# Reduce Health Over Time When Colliding With Object

Hi, I'm making a game where if you are in a specific radius of the enemy you will loose health over time. I am doing this by extending the range of the enemies collider with the 'Is Trigger' ticked. I have looked everywhere for a script that would work but none I have tried work for me. My question is: How might I be able to create this script?

If you need any more information do ask. Thanks, Joel.

 using UnityEngine;
 using System.Collections;
 
 public class Player_Health : MonoBehaviour {
 
     public static float curHealth = 100f;
     public static float maxHealth = 100f;
     public static float decHealth = 4f;
     public static float regHealth = 2f;
 
     void Start(){
         curHealth = 98f;
         }
 
     void Update(){
         if (curHealth < maxHealth) {
             curHealth += regHealth * Time.deltaTime;
             Debug.Log(curHealth);
         }
     }
 
     void OnCollisionStay2D(Collision2D other){
         if (other.gameObject.tag == "Darkness") {
             curHealth -= decHealth * Time.deltaTime;
             Debug.Log(curHealth);
         }
     }
 
 }

Here is all the code I could come up with by myself. At the moment I do regenerate health when it's less than 100 but when I enter the collider my health does not go down. Please help.

================================================================================================= Okay I got it working! Here's the code to help anyone else with the same problem:

 using UnityEngine;
 using System.Collections;
 
 public class Player_Health : MonoBehaviour {
 
     public static float curHealth = 100f;
     public static float maxHealth = 100f;
     public static float decHealth = 6f;
     public static float regHealth = 0.1f;
 
     void Start(){
         curHealth = 98f;
         }
 
     void Update(){
         if (curHealth < maxHealth) {
             curHealth += regHealth * Time.deltaTime;
             Debug.Log(curHealth);
         }
     }
 
     void OnTriggerStay2D(Collider2D other){
         if (other.gameObject.tag == "Darkness") {
             curHealth -= decHealth * Time.deltaTime;
             Debug.Log(curHealth);
         }
     }
 
 }