Lenders are growing wary of the riskier yet more flexible mortgages. They are making changes that could make it harder for borrowers to stretch into homes or refinance existing mortgages.

In December, federal banking regulators proposed guidelines to rein in lenders peddling loans that offer below-market introductory teaser rates, interest-only loans and payment-option loans that permit payments that don't cover even the interest. Just days before those long-anticipated guidelines were released, Washington Mutual, the nation's third-largest lender, acknowledged it had tightened its underwriting criteria on payment-option loans.

Piggyback loans that add a second loan for buyers who need to borrow the down payment are losing popularity according to Anthony Hsieh, president of LendingTree.com. Some lenders now require borrowers to pay off or refinance the balance of the second loan within two years.

Wells Fargo says it's getting a stream of calls from skittish homeowners holding these unconventional mortgages who want to refinance before their monthly payments vault.  The days of loose lending appear to be coming to an end.