String[] changedFields  = new String[]{};
for(WorkI_Item__c c: trigger.new){
    for(string s: fields){
        if(c.get(s) != trigger.oldMap.get(c.Id).get(s)){
            changedFields.add('Contact: ' + c.Id + ' - ' + s + ' - old:' + trigger.oldMap.get(c.Id).get(s) + ' new:' + c.get(s));
        }
    }
}
if(changedFields.size()>0){
    messaging.singleEmailMessage mail = new messaging.singleEmailMessage();
   // mail.setToAddresses(new string[]{UserInfo.getownerid()});
  //  mail.setReplyTo(UserInfo.getUserEmail());
    mail.setSubject('Cantact updated');

    string htmlBody = '';
    for (String s : changedFields){
        htmlBody += '<div>' + s + '</div>';
    }
    mail.setHtmlBody(htmlBody);
    Messaging.sendEmail(new Messaging.SingleEmailMessage[]{mail});
}