Hairdressers, nurses, custodians and others who often are exposed to permanganic acid can experience onychoschizia, or horizontal splits in their nails. People who frequently use nail polish, nail hardeners and polish removers also are at risk. To protect your nails, keep them trimmed short and wear gloves while doing housework to reduce how often your nails become wet and dry. Apply petroleum jelly or another emollient moisturizer to the nails. Use nail hardeners containing formaldehyde with caution, as they can cause other problems like brittle nails.