Mold can grow on paper because it is an organic material composed primarily of cellulose, which fungi use as a food source. Mold spores are ubiquitous in the air, remaining dormant until they land on an appropriate surface and are exposed to the correct environmental conditions. Since paper provides the necessary nutrients, the only remaining factor for growth is the presence of moisture.
The Essential Requirements for Mold Growth on Paper
Mold requires both a food source and sufficient moisture to transition from dormant spores to an active, growing colony. Paper, manufactured from wood pulp or other plant fibers, is rich in cellulose. Fungi release enzymes onto the paper’s surface, breaking down the cellulose and consuming the material, which causes permanent damage to the document or book.
The moisture level in the surrounding environment is the primary determinant of fungal activity. Mold growth can be triggered when the relative humidity (R.H.) exceeds 60% and is sustained for at least 48 hours. Paper products should be stored below 55% R.H. to prevent germination. While temperature is less important than moisture, most molds thrive between 40°F and 100°F, which is the same range humans prefer.
Recognizing Active Infestation
Identifying a mold infestation involves recognizing both visual and olfactory cues. Mold colonies typically appear as discolored spots or patches, varying widely depending on the species and paper type. Common colors include black, green, white, yellow, or powdery gray.
An active infestation often has a fuzzy or velvety texture because this visible growth is the mycelium and sporing structures. A strong, musty, or earthy odor is a telltale sign of mold, caused by microbial volatile organic compounds (mVOCs) released by the fungi. When mold is actively consuming the paper, it may feel wet or smear when touched, but dry, powdery growth is considered inactive or dormant.
Proactive Storage and Prevention
Controlling the storage environment is the most effective way to prevent mold growth on paper materials. The goal is to maintain a low and stable relative humidity, ideally between 30% and 50%. Using air conditioning or a dehumidifier is the most reliable way to achieve and maintain this low humidity level, especially in damp areas or during warm, humid seasons.
Adequate air circulation around stored items is important to prevent stagnant microclimates where moisture can accumulate. Paper should never be stored directly on a concrete floor, as this porous material can wick moisture up into boxes. Using archival-quality, acid-free boxes helps protect documents, and placing items several inches off the floor provides a buffer against potential water damage.
Safe Remediation and Disposal
Addressing mold on paper requires caution because disturbing the growth can release a high concentration of spores into the air, presenting a health risk. Before handling affected materials, personal protective equipment (PPE) should be worn, including disposable gloves and a mask approved for particle filtration. Active or wet mold must be dried out first in a low-humidity environment with gentle air circulation before cleaning is attempted.
For minor surface contamination on a dry item, a soft brush can be used to gently loosen the powdery mold, directing the debris into the nozzle of a HEPA vacuum cleaner. Cleaning with liquids like bleach, vinegar, or alcohol is discouraged for paper, as it can cause further damage, smearing, or staining. Items that are heavily water-damaged or extensively covered in mold should be sealed in a plastic bag and discarded to prevent the spread of spores. A professional conservator should be contacted for assistance with important or irreplaceable documents.