The under-sink cabinet is one of the more humid, cramped spots in a kitchen, thanks to the pipes running through it and the temperature swings from hot water use, which makes it a poor home for anything moisture-sensitive. Cleaning supplies, trash bags, and sturdy plastic bins tolerate the conditions well. Paper goods, cardboard packaging, and unsealed food items don't.
Why This Cabinet Behaves Differently From the Rest of the Kitchen
Every other cabinet in a kitchen is essentially a dry box. The one under the sink isn't, since it houses the plumbing for the faucet and often the garbage disposal, both of which introduce heat, moisture, and occasional condensation that the rest of the kitchen's storage never has to contend with. Treating this cabinet the same as any other storage space is how paper towel packaging ends up damp and cardboard boxes go soft at the bottom.
What Genuinely Belongs Here
Cleaning supplies are the obvious fit, since most are already designed to tolerate moisture and don't degrade from occasional humidity the way paper products do. Trash and recycling bins belong here too, both because of the plumbing access and because this is typically the closest point to where kitchen waste is generated. Sturdy plastic bins and caddies, used to corral smaller cleaning items, hold up fine in this environment since plastic doesn't absorb moisture the way cardboard or paper does.
What Struggles Here
Paper towels, napkins, and any paper-based packaging left in its original cardboard box tend to soften and occasionally mould if stored under the sink for extended periods, since cardboard readily absorbs ambient moisture. Unsealed food items, even shelf-stable ones, are a poor fit for the same reason: the humidity and occasional temperature swings aren't what most packaged food is designed to withstand.
Small appliances and anything with exposed metal parts are also a weak match for this cabinet, since the moisture that's manageable for plastic and sealed cleaning bottles can encourage rust or corrosion on metal surfaces over time.
Dealing With the Pipe Obstruction
The plumbing running through the cabinet breaks up the usable space into awkward sections rather than one open area, which is part of why this cabinet is so often just a loose pile rather than organized storage. A two-tier riser or a set of stackable bins built to work around the pipe shape reclaims some of that broken-up space, rather than leaving everything on the cabinet floor where the pipes make a single stack impossible.
Managing the Humidity Directly
A small moisture absorber, the kind used in closets and other damp spaces, placed at the back of this cabinet reduces the ambient humidity level meaningfully. This won't turn the cabinet into a fully dry storage space, but it narrows the gap enough that borderline items, a spare roll of paper towels, for instance, survive longer than they would otherwise.
A Cabinet That Needs Its Own Rules
The under-sink cabinet is a genuinely different environment from the rest of the kitchen's storage, and treating it that way, moisture-tolerant items in, paper and unsealed food out, prevents the slow degradation that happens when this cabinet gets stocked the same way as any other.