The most common cause of catfacing in tomatoes is exposure to temperatures below 50 degrees F during flowering and fruit set. Low temperatures inhibit pollination and cause the blossom to stick to the developing fruit. Both of these factors prevent certain parts of the fruit from developing. The undesirable scarring and indentation occurs when unaffected parts of the fruit continue to expand.
Tomatoes that develop during warm weather do not usually experience catfacing problems. However, evidence suggests that even when temperatures are warm, excessive soil nitrogen, exposure to the pesticide 2,4-D, and erratic soil moisture can cause catfacing.
Some cultivars and varieties, including many heirlooms, are more susceptible to catfacing. You can avoid the problem by choosing resistant varieties, such as 'Homestead' and 'Monte Carlo'. If your favorite varieties are susceptible but you'd still like to grow them, either protect your transplants with cloches in cold weather or wait until day and evening temperatures are consistently warm to plant them. Catfaced tomatoes are safe to eat; simply cut away the scarred areas.