Mildew

Mildew is an all-too-common affliction that plagues books and erodes their collectibility, value and preservation. A fungus caused by an abundance of moisture and lack of proper airflow, it can readily discolor and distort cloth and paper. Left unattended, mildew will progress and further damage a book. In addition, it can pose a health risk to those living around books that suffer from mildew.

While the damage caused by mildew is likely permanent, it is usually possible to arrest further degradation by removing mildew from the book.

Of course, prevention is always better than remediation and mildew can be avoided through proper care and storage of your books - i.e., ensuring that they are not exposed to extreme conditions, particularly dampness and that they are stored in such a way as to encourage proper airflow.

Below is an example of a book upon which mildew has caused discoloration of the cloth boards: