循环通过两个数组，而不将结果乘以第一个数组长度*第二个数组长度

I have two arrays responds back from server:

1. The list of all allergies that exist
2. The list of allergies in specific product

I need to display list of check-boxes of all allergies and mark the ones that exist in the other array as checked.

The second array can be null.

How can I loop through both arrays without multiplying the results by array1 * array2.

This code results into 8 check-box inputs because the list of all allergies is 4 and the product has only 2 allergies so the loop is executed 8 times!

<?php
$checked ="";
if (isset($allergies)) {  // array of all allergies
    foreach ($allergies as $key => $value) {
        if(isset ($productAllergies)) {  // array of product allergies
            foreach ($productAllergies as $productkey => $prodValue) {
                // echo 'product allergy'. $prodValue['allergy_id'] .' general'.$key ;
                if( $prodValue['allergy_id'] ==$key )
                    $checked ='checked';
                else
                    $checked ='';

?>
<?php
            } // foeach close
        } // if close ?>
            <input type="checkbox" name="allergy[]" value="<?php echo $key; ?>"  <?php echo $checked; ?>/> 
            <label>
                <?php echo $value; ?>
            </label>
<?php } // foreach close
} // if close
?>  

Can somebody help to clarify the logic I should follow to display the checkbox list with checked values.

If I understand the format properly this could work:

<?php
  $checked ="";     
  if (isset($allergies)) {  // array of all allergies
      foreach ($allergies as $key => $value) {

          if(isset ($productAllergies)){  // array of product allergies
              $k2 = array_search($key, $productAllergies);
              if (!empty($productAllergies[$k2])) {
                 $checked = 'checked';
              }
           }
       }

   }
  ?>