Weed, insect, and disease control may also be required for pastures. A healthy, productive pasture will resist invasion from most poisonous weeds and provide good quality forage. When pastures are overgrazed, horses will eat the grass and legume species down to the soil, which allows weeds to take over.
1 Melasma can be triggered by birth control pills because it increases hormones throughout the body. # 2  This is one of the most common causes of melasma. 3  Pregnancy: During pregnancy the body will become very hormonal and skin conditions like acne vulgaris and melasma/chloasma become very common.
Darker skinned individuals are more at risk than fair skinned individuals. Estrogen and progesterone sensitivity are also associated with the condition. This means birth control pills, pregnancy, and hormone therapy can all trigger melasma. Stress and thyroid disease have also been postulated to be causes of melasma. Sun exposure can also cause melasma because the ultraviolet rays affect the cells that control pigment (melanocytes).