The urea creams have been demonstrated to be very effective clinically for dry skin disorders that affect the feet. The urea is considered one of the better creams to use for this as different concentrations of the urea have different effects, so can be used depending on the nature of the skin condition.
The best urea cream for your feet is the one that matches the skin condition. The concentration of urea below around 20% are more useful to help to moisturize the skin and help the skin retain moisture. When the urea concentration is above 20% (eg the Walkers Urea 25), it is more helpful to both moisturize the skin and remove the dry skin. When the concentration gets up to 40%, it is more help to remove the dry and hard skin, especially that cracked skin around the heels. You need to use any one of those concentrations depending on what the conditions of your skin is and the desired effect.
