It turns out, you could do some of these.

$a = '10293';

var_dump(is_int($a)); // false
var_dump(is_numeric($a)); // true
var_dump(preg_match('/\d/', $a) === 1); // true

$b = 'foo';
var_dump(is_int($b)); // false
var_dump(is_numeric($b)); // false
var_dump(preg_match('/\d/', $b) === 1); // false


$c = 10293;
var_dump(is_int($c)); // true
var_dump(is_numeric($c)); // true
var_dump(preg_match('/\d/', $c) === 1); // true

PS: if you just want to make sure the number is a non-zero "number", you could do the following, or you could do as @cryode said, using the Validation Class. :D

if(intval(Input::get('skin')) > 0) { 
   ... 
}