Some scorch marks can be taken off white cotton by using 3 percent hydrogen peroxide. Apply to scorched area with an eye dropper until saturated. Leave on shirt for 20 minutes. If the stain still remains, repeat the process until it disappears. Rinse fabric in water.
Note: Some modern white fabrics have fluorescent brighteners, which react in the sun and may yellow; so read the care labels before treating white fabrics.