There a few ways you can straighten your hair without worrying about damaging your hair with heating irons. First, you can apply 1/3 cup milk from a spray bottle on your hair about 20-30 minutes before you shower. Use a wide tooth comb to comb your tangles out, then shampoo and condition as usual. This should last until the next time you wash your hair. You may also use castor oil before you blow dry your hair. You should apply the highest setting that your blow dryer has and use a comb to slowly work through your hair. This may not work for extremely curly hair.