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.
The incidence of melasma also increases in patients with thyroid disease. It is thought that the overproduction of melanocyte-stimulating hormone (MSH) brought on by stress can cause outbreaks of this condition. Other rare causes of melasma include allergic reaction to medications and cosmetics.