Guajava - Guajava demonstrates antifungal, antibacterial, anti-inflammatory, laxative, and analgesic properties. It is used to treat herpes ulcers, ringworm, dermatitis, and urinary tract infections. Guajava is related to cassia and senna, and contains anthraquinones found in those other species as well.
Vitamins B, particularly biotin (vitamin B7) and B12 are important to keep healthy nails. If your nutrition lacks in vitamins B, nails will be dry and brittle. Vitamin C deficiency is associated to brittle nails and may cause infections of nail tissues.
Deficiency of vitamin B and D cause pigmentation and ridges along the nail bed. The bluish black coloured vertical lines on your nails are warning alarms that you need to make immediate changes to your diet. Deficiency of vitamin C causes reddish black spots to appear on the nail bed and also leads to hang nails. Deficiency of vitamin A and D cause a situation called hapalonychia or soft nails.