There is absolutely no evidence that there are any foods that contribute to Pemphigus or Pemphigoid, however, particularly for those with mouth involvement, eating can be difficult and certain foods can aggravate the situation.
It is best to avoid:
Onions, garlic, chives, leeks, salt, oranges, tomatoes and tomato and brown sauce, marmalade, lemons, pizzas, pickles, vinegar, salad dressings, pre-prepared foods, some, cheeses (with high salt content), toast, crusty bread, berries, e.g. strawberry, blackberry, including strawberry yoghurt, all herbs and spices, fizzy drinks, crisps, nuts and hard food such as apples. Alcohol can dry out the mouth, particularly red wine.
When mouth lesions are particularly painful, try:-
eggs, fish, custard, ice cream, soft small pasta shells (take care about the sauce), soft vegetables (steamed to retain nutrients)
This can be difficult, although some restaurants will prepare a special simple dish omitting certain items. You need to be pro-active and ask for a dish without a certain item or sauce and check menus carefully for what is in each dish.
It is important to make sure you try to eat, even when it is difficult. Try using a small plastic spoon as it is softer on the mouth than metal cutlery
Vitamin and mineral supplements are reported to have positive effects, particularly Zinc. But the continued use of some drugs, mean that some additions are critical and others may help to restore depleted nutrients.
Calcium, for example, combined with D3 is essential to counteract the risk of osteosporosis that comes with long term use of steroids.
Some drugs have their own requirement for supplements. Methotrexate for example should be taken with Folic Acid.
It is worth reading the article Pemphigus in Remission for further thinking on the subject. http://www.pemphinremission.com/